Hypothalamic Areas Involved in Prostaglandin(PG)-Induced Gonadotropin Release. I: Effects of PGE2 and PGFga Implants on Luteinizing Hormone Release1 S. R. OJEDA, H. E. JAMESON, AND S. M. M C C A N N Department of Physiology, The University of Texas Health Science Center at Dallas, Southwestern Medical School, Dallas, Texas 75235 the ARH-ME clearly elevated LH titers. PGE2 implants located more than 1 mm lateral from the midline or outside the hypothalamus were ineffective. When PGE2 was placed in the preoptic area (POA) or anterior ventral portion of the anterior hypothalamic area (AHA), plasma LH levels rose strikingly, the first significant increase being observed at 20 min. PGE2 implants located in the vicinity of the paraventricular nucleus-dorsal portion of AHA were much less effective. PGF2a implanted in the ARH-ME or POA induced a small increase in plasma LH and the implantation of empty cannulae in the same areas was ineffective. Intrapituitary implants of PGE2 failed to alter plasma LH significantly. The results indicate that PGE2 acts at the ARH-ME region to induce LH release and that an even more effective site of action seems to be located in the POA-AHA. Since these are areas which contain LHRH, the results support the view that PGs can activate LHRH-secreting neurons in these regions. (Endocrinology 100: 1585, 1977)
ABSTRACT. Ovariectomized rats had a cannula inserted unilaterally within various hypothalamic areas. Several days later they were primed with a sc dose of 10 /u,g of estradiol benzoate (Eb). Two days after priming they were etherized and an initial blood sample was drawn from the external jugular vein. An inner cannula containing PGE2 or PGF2a at its tip was inserted into the previously implanted outer cannula. Blood samples were drawn at 20, 40, 60, and 120 min following the implantation. PGE2 induced a 4-5-fold increase in plasma LH 40 to 60 min following its implantation in the arcuate nucleus-median eminence region (ARH-ME). Levels were already significantly elevated at 20 min.When PGE2 was placed slightly more dorsally, close to the ventromedial nucleus (VMH), LH titers rose to comparable levels but only after a delay of 120 min. PGE2 implanted in the caudal portion of the ARH-ME or dorsally in the VMH-dorsomedial nuclei, barely increased plasma LH, whereas its placement in the anterior portion of
I
T NOW appears firmly established that prostaglandins (PGs), particularly those of the E series, can act centrally to stimulate pituitary LH release (1-8). Evidence for a physiological role of PGs in the release of gonadotropins has been provided by the earlier report of Orczyk and Behrman (9), who postulated that part of the suppressive effect of indomethacin on ovulation was due to a blockade of gonadotropin secretion, and by the more recent findings that inhibitors of PG synthesis can indeed block LH release in a variety of conditions (10,11). Evidence is also accumulating in favor of the view that the brain, presumably the hypothalamus, is the primary site of action for PG-induced gonadotropin release (1). Received October 8, 1976. 1 Supported by grants from NIH (AM 10073 and HD 05151) and by the Ford Foundation.
Intraventricular injection of PGE2 has been shown to evoke an increase in LHRH levels in hypophysial portal plasma (12) and in peripheral circulation (13), and to decrease hypothalamic content of the neurohormone (14). Furthermore, the administration of an anti-LHRH serum prevented PGE2-induced LH release (15,16). Intrapituitary injections of PGE2 cause LH release only under certain conditions of steroid priming (1,4), whereas direct infusion of the PG into the gland via a portal vessel failed to alter LH secretion (12). The aim of the present investigation was to define more clearly the hypothalamic areas where PGE 2 acts to evoke LH release. Consequently, the PG was unilaterally implanted in different sites of the hypothalamus and its effect on LH release was determined by radioimmunoassay. For comparison, PGF^ was also implanted in the hypothalamus. In addition, unilateral PGE 2
1585
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1586
OJEDA, JAiMESON AND M C C A N N
Enilo Vol !()()
1977 No 6
(0.5-0.6 ml) were obtained at 20, 40, 60, and 120 min following the implantation while the animal was lightly anesthetized with ether. After the last sample was drawn, the animals were decapitated and their heads placed in 10% Materials and Methods formaldehyde. Four to 8 days later the brains Virgin female Sprague-Dawley rats (Simonsen were carefully removed and placed in forLaboratories, Gilroy California), weighing 200- maldehyde for an additional period of 3-4 days. 220 g, were ovariectomized upon arrival and Thereafter, implant sites were verified in frontal housed under controlled conditions of light (14 h frozen sections of the brains which were cut at on, 10 h off) and temperature (24-26 C). Purina 60 fxm and studied under a stereoscopic microlaboratory chow and water were supplied ad lib- scope. The location of intrapituitary implants was itum. Fourteen to 21 days alter ovariectomy, the verified at necropsy by direct observation of the gland according to a procedure described earlier animals were used tor the experiments. (19). Implants were considered properly placed when tips of the cannulae extended into the tisExperimental procedures sue and were at least 0.5 mm from any edge of A 23 gauge stainless steel cannula (17 mm in the gland. length) was unilaterally implanted in the different areas of interest according to the co- Radioimmunoassay3 ordinates of De Groot's Atlas (18) using a stereoLH was assayed according to the method of taxic instrument (David Kopf). Cannulae were placed 3-4 days before the experiment. They Niswender et al. (20). The RP-1 rat pituitary LH were located at a distance of 0.5 mm from the reference standard was used and results were exmidline. For intrapituitary implants, a 23 gauge pressed in terms of tlie NIH-LH-S1 reference stainless steel cannula (17 mm in length) was preparation (1 ng NIH-LH-S1 = 33.3 ng LH unilaterally placed in one lobe of the anterior RP-1). pituitary gland at a distance of 1 mm from the midline. In order to increase responsiveness of Statistics the gonadotropin-releasing system to PGs (4), all Differences between hormone concentrations animals were injected with estradiol benzoate before and after implantation of PGs or empty (Eb, 10 /ag sc in 0.2 ml com oil) 48 h before tlie cannulae were analyzed by the paired t test. Difexperiment. erences between groups at different intervals On the day of the experiment, inner cannulae 2 post-injection were analyzed by the Student's t (18 mm in length), containing PGE2 or PGF^ test. at their tips, were prepared by gently tamping 30 gauge tubing (id 150 /xm) into a watch glass Results containing the PG. Material on the external surface of the tubing was carefully removed. After preparation of the inner cannula, each animal was Localization ofintrahypothalamic implants etherized, a blood sample (0.5-0.6 ml) was drawn of PGE2, PGF2a or empty cannula and their from the external jugular vein into heparinized effect on LH release syringes and tlie 30 gauge cannula containing tlie Mean preimplantation plasma LH values PG at the tip was inserted into the 23 gauge cannula which had been previously implanted. Since (n = 186) in the ovariectomized, estrogenthe inner cannula extended 1 mm beyond the primed rats were 4.0 ± 0.13 ng/ml. The imouter cannula and this could have produced non- plantation of an empty cannula in the arspecific alterations of gonadotropin release, control animals were implanted with empty inner 3 We are grateful to Dr. Niswender (Colorado cannulae. In all cases, additional blood samples implants were also placed in the anterior pituitary gland. A preliminary report of this study has appeared (17).
2
Prostaglandins E 2 and F2a were generously provided by Dr. J. E. Pike, The Upjohn Company, Kalamazoo, Michigan.
State University) for the supply of antiovine LH serum, and to Dr. L. Reichert (Emory University) for tlie supply of purified ovine LH for iodination. The rat reference was provided through the NIAMDDNIH Pituitary Hormone Program.
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PROSTAGLANDINS AND LH RELEASE
FIG. 1. Location of empty cannula implants projected on a parasagittal section through the rat brain. OC = optic chiasm; CA = anterior commissure; SC = suprachiasmatic nucleus; FX = fomix; PVH = paraventricular nucleus; AHA = anterior hypothalamic area; DMH = dorsomedial nucleus; VMH = ventromedial nucleus; ARH = arcuate nucleus; PH = posterior hypothalamic nucleus; MM = medial mammillary nucleus; AP = anterior pituitary; POA = preoptic area.
1587
OC
ARH A LH Following Empty Cannulo A More than 5 - less than 10 ng/ml • More than 2-less than 5 ng/ml o Between 0 - 2 ng/ml
cuate-median eminence (ARH-ME) region or the pre-optic area (POA) failed to elevate plasma LH. Only one animal out of 12 implanted in the ARH-ME region exhibited a maximal LH increase greater than 5 ng/ml
FiG. 2 Location of PGE2 implants projected on a parasagittal section through the rat brain. For definition of abbreviations, see legend to Fig. 1.
but less than 10 ng/ml (Fig. 1). Prostaglandin E2 implanted in the body of the median eminence-arcuate nucleus (BARH-ME) was highly effective in inducing LH release (Fig. 2). Seventeen out of 22 animals showed max-
OC
A LH Following PGE 2
A R H
* More than 20 ng/ml • More than 10 - less than 20 ng/ml A More than 5 - less than 10 ng/ml a More than 2 - l e s s than 5 ng/ml ° Between 0 - 2 ng/ml
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1588
OJEDA, JAMESON AND M C C A N N
imal LH increases greater than 10 ng/ml. The remaining 5 rats showed LH increases of intermediate magnitude. Four animals with PGE 2 implants located slightly more dorsally, in the arcuate-ventromedial nucleus area (ARH-VMH), showed LH increases greater than 10 ng/ml (Fig. 2). Interestingly, when PGE2 was placed in the postchiasmatic region-anterior portion of the arcuate nucleus (HARH-ME), 6 out of 12 animals showed LH increases greater than 10 ng/ml, whereas 4 of the other 6 also exhibited increments in plasma LH although of intermediate magnitude. Implants in the caudal portion of the arcuate nucleus-median eminence (TARH-post-ME) were much less effective. When PGE2 was implanted in the region of the preoptic area or ventral portion of the anterior hypothalamic area (POAVAHA), it evoked an even more remarkable elevation in plasma LH titers. Forty-seven out of 53 animals showed LH increases greater than 10 ng/ml. Prostaglandin E2 implants in areas comprising the paraventricular nucleus-dorsal portion of the anterior hypothalamic area (PVH-DAHA) or the ventromedial-dorsomedial nuclei (VMH-
Endo • 1977 Vol 100 • No 6
DMH) had little effect. In fact, only 5 rats with the PGE 2 implants located in the region of the PVH-DAHA showed LH increases greater than 10 ng/ml. Prostaglandin F ^ placed in the same areas where PGE 2 induced a remarkable elevation in plasma LH (POA and ARH-ME) was a much less effective stimulus for LH release (Fig. 3). Only 3 out of 17 rats with PGF^ implants in the ARH-ME region showed LH increases greater than 10 ng/ml. Likewise, only 4 out of 13 rats with PGF^ implanted in the POA-AHA showed LH increases greater than 10 ng/ml. None of the animals implanted with PGF^ showed an LH increase greater than 20 ng/ml, a result that was very frequently observed after PGE 2 (35 out of 53 in POA-VAHA; 9 out of 22 in the ARH-ME region). Time course of plasma LH following the intrahypothalamic implantation of PGE2, PGF2« or empty cannulae Prostaglandin E2 implanted in the BARHME induced a prompt rise in plasma LH which was already significant (P < 0.005) 20
FIG. 3. Location of PGF2a implants projected on a parasagittal section through the rat brain. For definition of abbreviations, see legend to Fig. 1.
00
ARH
A LH Following P 6 F 2 a * More than 20 ng/ml • More than 10 - less than 20 ng/ml A More than 5 - less than 10 ng/ml a More than 2 - less than 5 ng/ml o Between 0 - 2 ng/ml
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PROSTAGLANDINS AND LH RELEASE min following the implantation (Fig. 4, Panel A). Maximum levels were attained at 60 min ( P < 0.001). When PGE 2 implants were located slightly more dorsally (ARHVMH, 4 rats), LH was also elevated at 120 min to levels comparable to those produced by more ventral PGE 2 implants. However, the first significant increase (P < 0.001) was observed only after a delay of 40 min. Prostaglandin E 2 implanted in the HARHME induced a rapid increase in plasma LH at 20 min (P < 0.005) with peak levels being reached at 40-60 min (P < 0.01 and P < 0.001, respectively). Although PGE 2 implanted in the TARH-post-ME induced a significant elevation in plasma LH at 40 (P < 0.001), 60 (P < 0.005) and 120 min (P < 0.001), the magnitude of this elevation was much smaller (P < 0.005) than that induced by PGE 2 in BARH-ME. When PGE 2 A.
(2?.) •—•BARH-ME . ( 1 2 ) * — * HARM-ME O)D—OARH-VMH (16) o—oTARH-Po»l-ME (12)*—»0MH-VMH
20
I 15 < < 1
I
( 5 ) * - * B A R H - M E , >1mm lottrol (4)o—oOut ol MBH
1
-2
1
20
1
B. ,
1
40 60 TIME (min)
1
120
FIG. 4. Effect of PGE2 implants located in different regions of the medial basal hypothalamus on plasma LH levels of Ovx, Eb-treated rats. In this and subsequent figures, vertical lines represent standard error of the mean and numbers in parentheses indicate number of animals per group. BARH-ME = body of the arcuate nucleus-median eminence; HARH-ME = anterior portion of the arcuate nucleusanterior median eminence; TARH-post-ME = posterior portion of the arcuate nucleus-median eminence; ARH-VMH = arcuate-ventromedial nuclei; DMHVMH = dorsomedial-ventromedial nuclei; out of MBH = outside of the medial basal hypothalamus.
-
(13) (6)
1589
Ventrol (ont. lo«6.6) ventrol (post. to«6.6) 0orsol (AHA-PVH)
I30 - 25 x < 20 5
PGE2
-2
20
40 60 TIME (min)
120
FIG. 5. Effect of PGE2 implants located in the anterior hypothalamic area-paraventricular nucleus (AHA-PVH) on plasma LH levels of Ovx, EB-treated rats. Animals with implants in the ventral portion of AHA were grouped according to whether the implants were located anterior or posterior to the +6.6 vertical plane of De Groot's Atlas. Arrow indicates time of implantation.
was placed in the DMH-VMH areas, plasma LH levels barely increased at 60 (P < 0.025) and 120 min (P < 0.025). Prostaglandin E2 implants located outside the medial basal hypothalamus did not significantly alter plasma LH levels (Fig. 4, Panel B). When PGE 2 implants were located more than 1 mm from the midline, plasma LH levels rose gradually to become slightly but significantly elevated (P < 0.05) at 120 min (Fig. 4, Panel B). Prostaglandin E 2 placed in the anterior hypothalamic area-paraventricular nucleus (AHA-PVH) induced an increase in LH release whose magnitude varied according to the location of the implants (Figs. 2,5). The most effective implants were those located in the ventral portion of the AHA, anterior to the +6.6 horizontal plane of De Groot's Atlas. In these animals, LH levels were clearly elevated 40 min following the implantation (P < 0.001) and reached maximum values at 120 min ( P < 0.001). Implants located ventrally in the AHA but posterior to the +6.6 plane were less effective than those more rostrally placed, LH levels
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50
(18) o—oPGEo-POA (4)*—•PGE 2 -POA-AMA (11) »—*PGEz-Anl. POA (11)t>-
ABSTRACT. Ovariectomized rats had a cannula inserted unilaterally within various hypothalamic areas. Several days later they were primed with a sc dose of 10 /u,g of estradiol benzoate (Eb). Two days after priming they were etherized and an initial blood sample was drawn from the external jugular vein. An inner cannula containing PGE2 or PGF2a at its tip was inserted into the previously implanted outer cannula. Blood samples were drawn at 20, 40, 60, and 120 min following the implantation. PGE2 induced a 4-5-fold increase in plasma LH 40 to 60 min following its implantation in the arcuate nucleus-median eminence region (ARH-ME). Levels were already significantly elevated at 20 min.When PGE2 was placed slightly more dorsally, close to the ventromedial nucleus (VMH), LH titers rose to comparable levels but only after a delay of 120 min. PGE2 implanted in the caudal portion of the ARH-ME or dorsally in the VMH-dorsomedial nuclei, barely increased plasma LH, whereas its placement in the anterior portion of
I
T NOW appears firmly established that prostaglandins (PGs), particularly those of the E series, can act centrally to stimulate pituitary LH release (1-8). Evidence for a physiological role of PGs in the release of gonadotropins has been provided by the earlier report of Orczyk and Behrman (9), who postulated that part of the suppressive effect of indomethacin on ovulation was due to a blockade of gonadotropin secretion, and by the more recent findings that inhibitors of PG synthesis can indeed block LH release in a variety of conditions (10,11). Evidence is also accumulating in favor of the view that the brain, presumably the hypothalamus, is the primary site of action for PG-induced gonadotropin release (1). Received October 8, 1976. 1 Supported by grants from NIH (AM 10073 and HD 05151) and by the Ford Foundation.
Intraventricular injection of PGE2 has been shown to evoke an increase in LHRH levels in hypophysial portal plasma (12) and in peripheral circulation (13), and to decrease hypothalamic content of the neurohormone (14). Furthermore, the administration of an anti-LHRH serum prevented PGE2-induced LH release (15,16). Intrapituitary injections of PGE2 cause LH release only under certain conditions of steroid priming (1,4), whereas direct infusion of the PG into the gland via a portal vessel failed to alter LH secretion (12). The aim of the present investigation was to define more clearly the hypothalamic areas where PGE 2 acts to evoke LH release. Consequently, the PG was unilaterally implanted in different sites of the hypothalamus and its effect on LH release was determined by radioimmunoassay. For comparison, PGF^ was also implanted in the hypothalamus. In addition, unilateral PGE 2
1585
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1586
OJEDA, JAiMESON AND M C C A N N
Enilo Vol !()()
1977 No 6
(0.5-0.6 ml) were obtained at 20, 40, 60, and 120 min following the implantation while the animal was lightly anesthetized with ether. After the last sample was drawn, the animals were decapitated and their heads placed in 10% Materials and Methods formaldehyde. Four to 8 days later the brains Virgin female Sprague-Dawley rats (Simonsen were carefully removed and placed in forLaboratories, Gilroy California), weighing 200- maldehyde for an additional period of 3-4 days. 220 g, were ovariectomized upon arrival and Thereafter, implant sites were verified in frontal housed under controlled conditions of light (14 h frozen sections of the brains which were cut at on, 10 h off) and temperature (24-26 C). Purina 60 fxm and studied under a stereoscopic microlaboratory chow and water were supplied ad lib- scope. The location of intrapituitary implants was itum. Fourteen to 21 days alter ovariectomy, the verified at necropsy by direct observation of the gland according to a procedure described earlier animals were used tor the experiments. (19). Implants were considered properly placed when tips of the cannulae extended into the tisExperimental procedures sue and were at least 0.5 mm from any edge of A 23 gauge stainless steel cannula (17 mm in the gland. length) was unilaterally implanted in the different areas of interest according to the co- Radioimmunoassay3 ordinates of De Groot's Atlas (18) using a stereoLH was assayed according to the method of taxic instrument (David Kopf). Cannulae were placed 3-4 days before the experiment. They Niswender et al. (20). The RP-1 rat pituitary LH were located at a distance of 0.5 mm from the reference standard was used and results were exmidline. For intrapituitary implants, a 23 gauge pressed in terms of tlie NIH-LH-S1 reference stainless steel cannula (17 mm in length) was preparation (1 ng NIH-LH-S1 = 33.3 ng LH unilaterally placed in one lobe of the anterior RP-1). pituitary gland at a distance of 1 mm from the midline. In order to increase responsiveness of Statistics the gonadotropin-releasing system to PGs (4), all Differences between hormone concentrations animals were injected with estradiol benzoate before and after implantation of PGs or empty (Eb, 10 /ag sc in 0.2 ml com oil) 48 h before tlie cannulae were analyzed by the paired t test. Difexperiment. erences between groups at different intervals On the day of the experiment, inner cannulae 2 post-injection were analyzed by the Student's t (18 mm in length), containing PGE2 or PGF^ test. at their tips, were prepared by gently tamping 30 gauge tubing (id 150 /xm) into a watch glass Results containing the PG. Material on the external surface of the tubing was carefully removed. After preparation of the inner cannula, each animal was Localization ofintrahypothalamic implants etherized, a blood sample (0.5-0.6 ml) was drawn of PGE2, PGF2a or empty cannula and their from the external jugular vein into heparinized effect on LH release syringes and tlie 30 gauge cannula containing tlie Mean preimplantation plasma LH values PG at the tip was inserted into the 23 gauge cannula which had been previously implanted. Since (n = 186) in the ovariectomized, estrogenthe inner cannula extended 1 mm beyond the primed rats were 4.0 ± 0.13 ng/ml. The imouter cannula and this could have produced non- plantation of an empty cannula in the arspecific alterations of gonadotropin release, control animals were implanted with empty inner 3 We are grateful to Dr. Niswender (Colorado cannulae. In all cases, additional blood samples implants were also placed in the anterior pituitary gland. A preliminary report of this study has appeared (17).
2
Prostaglandins E 2 and F2a were generously provided by Dr. J. E. Pike, The Upjohn Company, Kalamazoo, Michigan.
State University) for the supply of antiovine LH serum, and to Dr. L. Reichert (Emory University) for tlie supply of purified ovine LH for iodination. The rat reference was provided through the NIAMDDNIH Pituitary Hormone Program.
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PROSTAGLANDINS AND LH RELEASE
FIG. 1. Location of empty cannula implants projected on a parasagittal section through the rat brain. OC = optic chiasm; CA = anterior commissure; SC = suprachiasmatic nucleus; FX = fomix; PVH = paraventricular nucleus; AHA = anterior hypothalamic area; DMH = dorsomedial nucleus; VMH = ventromedial nucleus; ARH = arcuate nucleus; PH = posterior hypothalamic nucleus; MM = medial mammillary nucleus; AP = anterior pituitary; POA = preoptic area.
1587
OC
ARH A LH Following Empty Cannulo A More than 5 - less than 10 ng/ml • More than 2-less than 5 ng/ml o Between 0 - 2 ng/ml
cuate-median eminence (ARH-ME) region or the pre-optic area (POA) failed to elevate plasma LH. Only one animal out of 12 implanted in the ARH-ME region exhibited a maximal LH increase greater than 5 ng/ml
FiG. 2 Location of PGE2 implants projected on a parasagittal section through the rat brain. For definition of abbreviations, see legend to Fig. 1.
but less than 10 ng/ml (Fig. 1). Prostaglandin E2 implanted in the body of the median eminence-arcuate nucleus (BARH-ME) was highly effective in inducing LH release (Fig. 2). Seventeen out of 22 animals showed max-
OC
A LH Following PGE 2
A R H
* More than 20 ng/ml • More than 10 - less than 20 ng/ml A More than 5 - less than 10 ng/ml a More than 2 - l e s s than 5 ng/ml ° Between 0 - 2 ng/ml
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1588
OJEDA, JAMESON AND M C C A N N
imal LH increases greater than 10 ng/ml. The remaining 5 rats showed LH increases of intermediate magnitude. Four animals with PGE 2 implants located slightly more dorsally, in the arcuate-ventromedial nucleus area (ARH-VMH), showed LH increases greater than 10 ng/ml (Fig. 2). Interestingly, when PGE2 was placed in the postchiasmatic region-anterior portion of the arcuate nucleus (HARH-ME), 6 out of 12 animals showed LH increases greater than 10 ng/ml, whereas 4 of the other 6 also exhibited increments in plasma LH although of intermediate magnitude. Implants in the caudal portion of the arcuate nucleus-median eminence (TARH-post-ME) were much less effective. When PGE2 was implanted in the region of the preoptic area or ventral portion of the anterior hypothalamic area (POAVAHA), it evoked an even more remarkable elevation in plasma LH titers. Forty-seven out of 53 animals showed LH increases greater than 10 ng/ml. Prostaglandin E2 implants in areas comprising the paraventricular nucleus-dorsal portion of the anterior hypothalamic area (PVH-DAHA) or the ventromedial-dorsomedial nuclei (VMH-
Endo • 1977 Vol 100 • No 6
DMH) had little effect. In fact, only 5 rats with the PGE 2 implants located in the region of the PVH-DAHA showed LH increases greater than 10 ng/ml. Prostaglandin F ^ placed in the same areas where PGE 2 induced a remarkable elevation in plasma LH (POA and ARH-ME) was a much less effective stimulus for LH release (Fig. 3). Only 3 out of 17 rats with PGF^ implants in the ARH-ME region showed LH increases greater than 10 ng/ml. Likewise, only 4 out of 13 rats with PGF^ implanted in the POA-AHA showed LH increases greater than 10 ng/ml. None of the animals implanted with PGF^ showed an LH increase greater than 20 ng/ml, a result that was very frequently observed after PGE 2 (35 out of 53 in POA-VAHA; 9 out of 22 in the ARH-ME region). Time course of plasma LH following the intrahypothalamic implantation of PGE2, PGF2« or empty cannulae Prostaglandin E2 implanted in the BARHME induced a prompt rise in plasma LH which was already significant (P < 0.005) 20
FIG. 3. Location of PGF2a implants projected on a parasagittal section through the rat brain. For definition of abbreviations, see legend to Fig. 1.
00
ARH
A LH Following P 6 F 2 a * More than 20 ng/ml • More than 10 - less than 20 ng/ml A More than 5 - less than 10 ng/ml a More than 2 - less than 5 ng/ml o Between 0 - 2 ng/ml
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PROSTAGLANDINS AND LH RELEASE min following the implantation (Fig. 4, Panel A). Maximum levels were attained at 60 min ( P < 0.001). When PGE 2 implants were located slightly more dorsally (ARHVMH, 4 rats), LH was also elevated at 120 min to levels comparable to those produced by more ventral PGE 2 implants. However, the first significant increase (P < 0.001) was observed only after a delay of 40 min. Prostaglandin E 2 implanted in the HARHME induced a rapid increase in plasma LH at 20 min (P < 0.005) with peak levels being reached at 40-60 min (P < 0.01 and P < 0.001, respectively). Although PGE 2 implanted in the TARH-post-ME induced a significant elevation in plasma LH at 40 (P < 0.001), 60 (P < 0.005) and 120 min (P < 0.001), the magnitude of this elevation was much smaller (P < 0.005) than that induced by PGE 2 in BARH-ME. When PGE 2 A.
(2?.) •—•BARH-ME . ( 1 2 ) * — * HARM-ME O)D—OARH-VMH (16) o—oTARH-Po»l-ME (12)*—»0MH-VMH
20
I 15 < < 1
I
( 5 ) * - * B A R H - M E , >1mm lottrol (4)o—oOut ol MBH
1
-2
1
20
1
B. ,
1
40 60 TIME (min)
1
120
FIG. 4. Effect of PGE2 implants located in different regions of the medial basal hypothalamus on plasma LH levels of Ovx, Eb-treated rats. In this and subsequent figures, vertical lines represent standard error of the mean and numbers in parentheses indicate number of animals per group. BARH-ME = body of the arcuate nucleus-median eminence; HARH-ME = anterior portion of the arcuate nucleusanterior median eminence; TARH-post-ME = posterior portion of the arcuate nucleus-median eminence; ARH-VMH = arcuate-ventromedial nuclei; DMHVMH = dorsomedial-ventromedial nuclei; out of MBH = outside of the medial basal hypothalamus.
-
(13) (6)
1589
Ventrol (ont. lo«6.6) ventrol (post. to«6.6) 0orsol (AHA-PVH)
I30 - 25 x < 20 5
PGE2
-2
20
40 60 TIME (min)
120
FIG. 5. Effect of PGE2 implants located in the anterior hypothalamic area-paraventricular nucleus (AHA-PVH) on plasma LH levels of Ovx, EB-treated rats. Animals with implants in the ventral portion of AHA were grouped according to whether the implants were located anterior or posterior to the +6.6 vertical plane of De Groot's Atlas. Arrow indicates time of implantation.
was placed in the DMH-VMH areas, plasma LH levels barely increased at 60 (P < 0.025) and 120 min (P < 0.025). Prostaglandin E2 implants located outside the medial basal hypothalamus did not significantly alter plasma LH levels (Fig. 4, Panel B). When PGE 2 implants were located more than 1 mm from the midline, plasma LH levels rose gradually to become slightly but significantly elevated (P < 0.05) at 120 min (Fig. 4, Panel B). Prostaglandin E 2 placed in the anterior hypothalamic area-paraventricular nucleus (AHA-PVH) induced an increase in LH release whose magnitude varied according to the location of the implants (Figs. 2,5). The most effective implants were those located in the ventral portion of the AHA, anterior to the +6.6 horizontal plane of De Groot's Atlas. In these animals, LH levels were clearly elevated 40 min following the implantation (P < 0.001) and reached maximum values at 120 min ( P < 0.001). Implants located ventrally in the AHA but posterior to the +6.6 plane were less effective than those more rostrally placed, LH levels
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