Europ. J. Cancer Vol. 12, pp. 679-682. Pergamon Press 1976. Printed in Great Britain
General Papers In Vitro Effects of Prolactin upon Testosterone Metabolism by Rat Mammary Adenocarcinomata* WILLIAM R. MILLER Department of Clinical Surgery, University Medical School, Edinburgh EH8 9AG, Great Britain A b s t r a c t - - T h e ,ffects of in vitro addition of prolactin (50 pg/ml) upon the conversion of testosterone to 5a dihydrotestosterone (5a D H T ) and 5~ androstanediol by incubates of rat mammary carcinomas have been investigated. The studies have beenperformed on (a) primary adenocarcinomata induced by the carcinogen 7,12-dimethylbenzanthracene (DMBA) in female Sprague-Dawley rats, and (b) transplantable tumours obtained by serial transplantation of a further DMBA-induced tumour into neonatal& thymectomized rats. In incubations of primary DMBA-induced tumours, addition of prolactin inhibited the production of both 5a D H T and 5a androstanediol, the overall 5~ reduction being between 27 and 40 ~o lower than that in control incubations. In contrast, prolactin failed to inhibit, and in some cases stimulated, the 5a reduction of testosterone in the transplantable tumour.
INTRODUCTION
MATERIAL AND M E T H O D S
BOTH PROLACTE.~I and steroid hormones are known to influence the growth and development of rat manamary tumours [1-3]. In the DMBA treated rat, there appears to be a direct correlation between plasma prolactin levels and the genetically determined susceptibility to m a m m a r y cancer [4]. Elevation of plasma prolactin levels accelerates the growth of m a m m a r y tumours [5-7] and conversely lowered levels raay cause tumour regression [8]. Similarly, administration of steroids of the androstane series such as 5a dihydrotestosterone m a y inhibit the growth of m a m m a r y tumours in the rat [9, 10]. The aim of th.e present study was to determine the in vitro effects of prolactin, upon the production of 5a androstane steroids by rat m a m m a r y tumours.
Tumour tissue (a) DMBA-induced tumours. R a n d o m bred female Sprague-Dawley rats were given 5 mg dimethylbenzanthracene (DMBA) intravenously at 50 days of age. Subsequently induced m a m m a r y tumours were allowed to grow to 2 x 2 cm in size. At this stage, three rats were sacrificed by exsanguination and the tumours incubated; three others were sequentially oophorectomised and given oestradiol-17fl (1/~g) to determine tumour hormone dependence. All tumours regressed after oophorectomy but renewed growth following oestrogen administration and were therefore hormone dependent. (b) Transplanted tumours ( TG 3). The tumour studied was originally induced by DMBA as above, in an inbred Sprague-Dawley rat (ADILA) [4]. It was serially transplanted into further A D R A rats (neonatally thymectomized) by dorsal skin implantation and studied at its 2rid and 6th passages. Although all the tumours investigated were derived from intact rats, the
Accepted April 1, 1976. *This work was performed with a grant from the Cancer Research Campaign, grant number SP 1256. 679
680
William R. Miller
same tumour at its 6th passage in other rats, failed to regress following oophorectomy but was stimulated by oestradiol (1 #g daily). Tumour growth was therefore independent of oophorectomy but sensitive to oestradiol.
Tumour processing and incubation All tumours were processed at 0°C until incubation was carried out (within 30 min of tissue removal). One gram of each tumour was finely sliced and Krebs Ringer phosphate buffer pH 7.4 (10 ml), an NADPH generating system (200 ~ mol glucose-6-phosphate, 25 mg NADP, and 50 units glucose-6-phosphate dehydrogenase) and the radioactive precursor (45 gCi 7e-3H testosterone) added. Duplicate incubations were set up with the addition of either ovine prolactin, rat prolactin or rat growth hormone (50pg/ml). The tumour slices were then incubated by shaking at 37°C in an atmosphere of oxygen for i hr. The reaction was stopped by adding methanol to 80 % (v/v) and the incubations stored at - 10°C until processed.
Purification and characterization of metabolites Before extraction, 500 #g of non-radioactive carrier steroids were added to monitor recovery losses. The metabolites were extracted, separated into individual steroids and purified by thin layer chromatography, as described previously [11]. The percentage of metabolism of testosterone and conversion to 5e DHT and 5e androstanediol were determined by measuring the percentage of incorporation of radioactive label into the appropriate metabolites after correction for recovery losses.
RESULTS The effects on testosterone metabolism of in vitro addition of prolactin to incubations of DMBA-induced tumours are presented in Table 1. No consistent effects were produced by prolactin on the absolute level of testosterone metabolised. Prolactin, however, inhibited the conversion of testosterone to both 5a DHT and 5a androstanediol. Estimates of total 5a reduction obtained by combining the production of 5~ DHT with that of 5~ androstanediol showed that prolactin produced a consistent inhibition of 5~ reduction (27.4 A.9.3~o of control incubations), irrespective of the type of prolactin used, or whether the tumour was obtained from intact, or endocrine manipulated rats. Similar in vitro addition of rat growth
hormone at the same concentration had negligible effects in 4 tumours and inhibited 5a reduction in only one tumour (to a lesser extent than prolactin). The results of similar studies using the transplanted tumour are presented in Table 2. In these incubations, the overall level of testosterone metabolism was extremely high and relatively unaffected by the addition of prolactin. In contrast to the primary DMBA tumours, in this transplanted tumour, prolactin tended to increase the percentage of production of 5~ DHT and total 5a reduction of testosterone.
DISCUSSION The results presented in this study indicate that the 5~ reduction of testosterone by rat mammary carcinomas may be influenced by the in vitro addition of either rat or ovine prolactin. These effects may be partially specific to prolactin as the in vitro addition of growth hormone at the same concentration had less or no effect on testosterone metabolism. In primary DMBA-induced tumours, prolactin consistently inhibited the production of 5~ reduced metabolites of testosterone. This is interesting in view of the inhibitory properties of the 5~ androstane steroids on the growth of hormone dependent rat mammary tumours [9, 10]. Although evidence for hormone dependence was obtained for only three of the DMBA tumours studied in this series, it was our experience that the majority of DMBA tumours induced in this group of animals were hormone dependent. It would therefore be in keeping with the growth promoting effects of prolactin on hormone dependent tumours that protactin should inhibit the production of 5~ reduced steroids at tumour level. The results from in vitro incubations of the transplanted tumour differ from the primary DMBA tumours in two major respects. Firstly, although the DNA content and cellularity of the two groups of tumours were similar, the overall metabolism and 5~ reduction of testosterone in control incubations was, in general, higher in the transplanted tumour. Secondly, prolactin tended to stimulate 5~ reduction in the transplanted tumour in diret contrast to its inhibitory effects in the primary tumours. Several factors may be implicated in these differences between transplanted and DMBA tumours. Firstly, whereas the DMBA tumours are likely to be hormone dependent, the transplanted tumour failed to regress following
I n Vitro Effects of Prolactin
681
Table 1. Metabolism of 7~-3H testosterone by DMBA induced tumours Per cent testosterone metabolised
Rat
A* B]' C* D]. E* Ft
Control + proh, ctin (rat) + growth hormone Control + prolactin (rat) + growth hormone Control + prolactin (rat) + growth hormone Control + prolactin (rat) Control + prolactin (ovine) + growth hormone Control + prolaetin (ovlne) + growth hormone
94-80 85"00 90.20 46.50 35.10 46.10 47.45 43.10 48.20 42-50 37.10 33.85 34.75 31.60 47.80 59.40 44.45
Per cent conversion to 5= DHT
28.50 13.20 24.20 5.50 (-24.5) 3.90 (-0.9) 6.20 16.15 (-9.2) 8.40 (+ 1.6) 13.60 5.05 (-12.6) 2.50 5.65 (+ 2.6) 5.50 - 6.7) 5.00 19.20 +24"3) 9.40 -7.0) 19.40 (-10.3) ( - 4.9)
(-53.6) (-15.1) (-29.1) (+12.7) (-49.0) (-15.8) (-50.5) (-2"7) (-11.5) (-51.1) (-t-1.0)
Per cent conversion to 5= androstanediol 25.40 21.30 22.10 27.05 17-00 26.70 14.15 13.55 17.20 20.10 13.30 12.45 7.60 11.55 11.20 8.75 3.95
Per cent 5= reduction
53.90 34.50 46.30 32.55 (-37.2) 20.90 (-1.3) 32.90 30.30 (-4.2) 21.95 (+21.55) 30.80 25.15 (-33.8) 15.80 18.10 (-39"0) 13.10 ( - 7"2) 16.55 30.40 (-21"9) 18.15 (-64.7) 23.35 (-16.1) (-13.0)
(-36.0) (-14.1) (-35.8) (+ 1.1) (-27.6) (+ 1.7) (-37.2) (-27"6) ( - 8.6) (-40.3) (-23.2)
Figures in parentheses represent the percentage of change caused by addition of prolactin or growth hormone (50/~g/ml). *Intact rat. ]'Rat sequentially oophorectomized and given oestradiol (1 pg daily).
Table 2.
Per cent testosterone metabolised
Rat 1" 2* 3* 4t 5].
Metabolism of 70~-3H testosterone by transplanted tumogrs
Control +prolactin(ovine) Control + prolactin (ovine) Control +prolactin(ovine) Control + prolactin (rat) Control +prolactin(rat)
88"70 95.50 96.80 97.15 98.70 95.50 94.00 97.00 96.70 88.05
Per cent conversion to 5= DHT
19.90 26"50 9"65 (+0.3) 21'90 13"30 ( - 3 " 3 ) 16.50 9.50 (+ 3"I) 24.50 3.40 (-9.0) 5"25
(+7.7)
Per cent conversion to 5~ androstanediol
31.30 (+ 33"2) 59.00 33"60 (+127.0) 30"30 66.15 (+ 24"0) 66.10 39.20 (+158.0) 31.70 50.70 (+ 54.4) 55.10
(+88"5) ( - 9.8) (0) (-19.1) (+ 8.6)
Per cent 5g reduction 51.20 85.50 43.25 52.20 79.45 82.60 48.70 56.20 54.10 60.35
(+67.0) (+20.7) (+ 4.0) (+ 15.4) (+11.6)
*Tumour at 2nd passage. 1"Tumour at 6th passage. Figures in parentheses represent % change caused by addition of prolactin.
o o p h o r e c t o m y ; the effects o f prolactin m a y therefore reflec~ differences between h o r m o n e d e p e n d e n t and. h o r m o n e sensitive tumours. Secondly, there are different circulating prolactin levels in the two strains o f rats u s e d - the A D R A strain, in which the t r a n s p l a n t e d t u m o u r was i n d u c e d a n d subsequently transp l a n t e d , has a lower basal level o f circulating prolactin, in c o m p a r i s o n with the r a n d o m -
b r e d variety in which the p r i m a r y D M B A t u m o u r s were i n d u c e d [4]. A t present, it is not possible to r e m o v e the strain difference as t u m o u r i n d u c t i o n rate b y D M B A in the A D R A r a t is exceptionally low a n d the t r a n s p l a n t e d t u m o u r is not a c c e p t e d b y r a n d o m l y b r e d animals. I n conclusion, it is w o r t h emphasizing t h a t whilst prolactin has a l r e a d y been shown to
682
William R. Miller
affect steroid metabolism in other tissues, such as the prostate [12] and testis [13], its effects in m a m m a r y tumour tissue m a y assume added importance in view of the properties of the 5~ reduced metabolites involved to influence tumour growth.
Acimowledgements--The author thanks Professor A. P. M. Forrest for his interest and encouragement, the Cancer Research Campaign for the Grant to Professor Forrest supporting this work and Miss J. Telford for her technical assistance. Rat and ovine prolactin and rat growth hormone were gifts from the National Institutes of Health (Bethesda, Maryland).
REFERENCES 1.
2. 3.
4.
5. 6. 7. 8.
9. 10. 11. 12.
13.
T . L . DAO and D. SINI-IA, In Fourth Tenovus Workshop, Prolactin and Carcinogenesis--Oestrogen and Prolactin in Mammary Carcinogenesis in vivo and in vitro Studies. (Edited by A. R. BOYNSand K. GRIFFITHS),p. 199. Alpha Omega Alpha Publishing, Cardiff, U.K. (1972). J. MEiaxs, In Fourth Tenovus Workshop, Prolactin and Carcinogenesis--Section 2, Introduction. (Edited by A. R. BoYNs and K. GRnoI~ITX-IS),p. 54. Alpha Omega Alpha Publishing, Cardiff, U.K. (1972). O . H . PEARSON, R. L. M. MURRAY,G. MOZAI~FARIANand J. PENSKY,In Fourth Tenovus Workshop, Prolactin and Carcinogenesis--Prolactin and Experimental Breast Cancer. (Edited by A. R. BOYNS and K. GRIFFITrlS). p. 154. Alpha Omega Alpha Publishing, Cardiff, U.K. (1972). A . R . BOYNS,R. BUCHAN,E. N. COLE, A. P. M. FORRESTand K. GRIFFITHS, Basal prolactin blood levels in three strains of rat with differing incidence of 7,12-dimethylbenz(a)anthracene induced mammary turnouts. Europ. 3.. Cancer 9, 169 (1973). J . A . CLEMENS,C. W. W~LSCHand J. MEITES, Effects of hypothalmic lesions on incidence and growth of mammary turnouts in carcinogen-treated rats. Proc. Soc. exp. Biol.(N.Y.) 127, 969 (1968). C . W . WELSCH,J. A. CLEMENSand J. MEITES, Effects of multiple pituitary homografts or progesterone on 7,12-dimethylbenz(a)anthracene-induced mammary turnouts in rats. d. nat. Cancer Inst. 41, 465 (1968). C.W. WELSCHand J. MEITES, Effects of a norethylnodrel-mestranol combination (Enovid) on development and growth of carcinogen-induced mammary turnouts in female rats. Cancer (Philad.) 23, 601 (1969). E . E . CASSELL,J. MEITES and C. W. WELSCH, Effects of ergocornine and ergocryptine on growth of 7,12-dimethylbenz(a)anthracene-induced mammary tumours in rats. Cancer Res. 31, 1051 (1971). C. HUOOlNS, 13. BRIZlARELLIand H. SUTTON, Rapid induction of mammary carcinoma in the rat and the influence of hormones on the turnouts. J. exp. Med. 109, 25 (1959). C. HUOOlNS and K. MAINZER, Hormonal influence on mammary tumours of the rat. II. Retardation of growth of a transplanted fibroadenoma in intact female rats by steroids in the androstane series, d. exp. Med. 105, 485 (1957). W . R . MILLER,A. P. M. FORRESTand T. HAMILTON,Steroid metabolism by human breast and rat mammary carcinomata. Steroids 23, 379 (1974). A . R . BoYNs, E. N. COLE, M. P. GOLDER,V. DANUTRA, M. E. HARPER, B. BROWNSEY,T. COWLEY, G. E. JONES and K. GRIFFITHS,In Fourth Tenovus Workshop, Prolactin and Carcinogenesis--Prolactin studies with the prostate. (Edited by A. R. BoYNs and K. GRIFFITHS).Alpha Omega Alpha Publishing, Cardiff, U.K. (1972). A . A . HArlEZ, C. W. LLOYD and W. BARTIE, The role of prolactin in the regulation of testis function: the effects of prolactin and luteinizing hormone on the plasma levels of testosterone and androstenedione in hypophysectomized rats. d. Endocr. 52,, 327 (1972).
General Papers In Vitro Effects of Prolactin upon Testosterone Metabolism by Rat Mammary Adenocarcinomata* WILLIAM R. MILLER Department of Clinical Surgery, University Medical School, Edinburgh EH8 9AG, Great Britain A b s t r a c t - - T h e ,ffects of in vitro addition of prolactin (50 pg/ml) upon the conversion of testosterone to 5a dihydrotestosterone (5a D H T ) and 5~ androstanediol by incubates of rat mammary carcinomas have been investigated. The studies have beenperformed on (a) primary adenocarcinomata induced by the carcinogen 7,12-dimethylbenzanthracene (DMBA) in female Sprague-Dawley rats, and (b) transplantable tumours obtained by serial transplantation of a further DMBA-induced tumour into neonatal& thymectomized rats. In incubations of primary DMBA-induced tumours, addition of prolactin inhibited the production of both 5a D H T and 5a androstanediol, the overall 5~ reduction being between 27 and 40 ~o lower than that in control incubations. In contrast, prolactin failed to inhibit, and in some cases stimulated, the 5a reduction of testosterone in the transplantable tumour.
INTRODUCTION
MATERIAL AND M E T H O D S
BOTH PROLACTE.~I and steroid hormones are known to influence the growth and development of rat manamary tumours [1-3]. In the DMBA treated rat, there appears to be a direct correlation between plasma prolactin levels and the genetically determined susceptibility to m a m m a r y cancer [4]. Elevation of plasma prolactin levels accelerates the growth of m a m m a r y tumours [5-7] and conversely lowered levels raay cause tumour regression [8]. Similarly, administration of steroids of the androstane series such as 5a dihydrotestosterone m a y inhibit the growth of m a m m a r y tumours in the rat [9, 10]. The aim of th.e present study was to determine the in vitro effects of prolactin, upon the production of 5a androstane steroids by rat m a m m a r y tumours.
Tumour tissue (a) DMBA-induced tumours. R a n d o m bred female Sprague-Dawley rats were given 5 mg dimethylbenzanthracene (DMBA) intravenously at 50 days of age. Subsequently induced m a m m a r y tumours were allowed to grow to 2 x 2 cm in size. At this stage, three rats were sacrificed by exsanguination and the tumours incubated; three others were sequentially oophorectomised and given oestradiol-17fl (1/~g) to determine tumour hormone dependence. All tumours regressed after oophorectomy but renewed growth following oestrogen administration and were therefore hormone dependent. (b) Transplanted tumours ( TG 3). The tumour studied was originally induced by DMBA as above, in an inbred Sprague-Dawley rat (ADILA) [4]. It was serially transplanted into further A D R A rats (neonatally thymectomized) by dorsal skin implantation and studied at its 2rid and 6th passages. Although all the tumours investigated were derived from intact rats, the
Accepted April 1, 1976. *This work was performed with a grant from the Cancer Research Campaign, grant number SP 1256. 679
680
William R. Miller
same tumour at its 6th passage in other rats, failed to regress following oophorectomy but was stimulated by oestradiol (1 #g daily). Tumour growth was therefore independent of oophorectomy but sensitive to oestradiol.
Tumour processing and incubation All tumours were processed at 0°C until incubation was carried out (within 30 min of tissue removal). One gram of each tumour was finely sliced and Krebs Ringer phosphate buffer pH 7.4 (10 ml), an NADPH generating system (200 ~ mol glucose-6-phosphate, 25 mg NADP, and 50 units glucose-6-phosphate dehydrogenase) and the radioactive precursor (45 gCi 7e-3H testosterone) added. Duplicate incubations were set up with the addition of either ovine prolactin, rat prolactin or rat growth hormone (50pg/ml). The tumour slices were then incubated by shaking at 37°C in an atmosphere of oxygen for i hr. The reaction was stopped by adding methanol to 80 % (v/v) and the incubations stored at - 10°C until processed.
Purification and characterization of metabolites Before extraction, 500 #g of non-radioactive carrier steroids were added to monitor recovery losses. The metabolites were extracted, separated into individual steroids and purified by thin layer chromatography, as described previously [11]. The percentage of metabolism of testosterone and conversion to 5e DHT and 5e androstanediol were determined by measuring the percentage of incorporation of radioactive label into the appropriate metabolites after correction for recovery losses.
RESULTS The effects on testosterone metabolism of in vitro addition of prolactin to incubations of DMBA-induced tumours are presented in Table 1. No consistent effects were produced by prolactin on the absolute level of testosterone metabolised. Prolactin, however, inhibited the conversion of testosterone to both 5a DHT and 5a androstanediol. Estimates of total 5a reduction obtained by combining the production of 5~ DHT with that of 5~ androstanediol showed that prolactin produced a consistent inhibition of 5~ reduction (27.4 A.9.3~o of control incubations), irrespective of the type of prolactin used, or whether the tumour was obtained from intact, or endocrine manipulated rats. Similar in vitro addition of rat growth
hormone at the same concentration had negligible effects in 4 tumours and inhibited 5a reduction in only one tumour (to a lesser extent than prolactin). The results of similar studies using the transplanted tumour are presented in Table 2. In these incubations, the overall level of testosterone metabolism was extremely high and relatively unaffected by the addition of prolactin. In contrast to the primary DMBA tumours, in this transplanted tumour, prolactin tended to increase the percentage of production of 5~ DHT and total 5a reduction of testosterone.
DISCUSSION The results presented in this study indicate that the 5~ reduction of testosterone by rat mammary carcinomas may be influenced by the in vitro addition of either rat or ovine prolactin. These effects may be partially specific to prolactin as the in vitro addition of growth hormone at the same concentration had less or no effect on testosterone metabolism. In primary DMBA-induced tumours, prolactin consistently inhibited the production of 5~ reduced metabolites of testosterone. This is interesting in view of the inhibitory properties of the 5~ androstane steroids on the growth of hormone dependent rat mammary tumours [9, 10]. Although evidence for hormone dependence was obtained for only three of the DMBA tumours studied in this series, it was our experience that the majority of DMBA tumours induced in this group of animals were hormone dependent. It would therefore be in keeping with the growth promoting effects of prolactin on hormone dependent tumours that protactin should inhibit the production of 5~ reduced steroids at tumour level. The results from in vitro incubations of the transplanted tumour differ from the primary DMBA tumours in two major respects. Firstly, although the DNA content and cellularity of the two groups of tumours were similar, the overall metabolism and 5~ reduction of testosterone in control incubations was, in general, higher in the transplanted tumour. Secondly, prolactin tended to stimulate 5~ reduction in the transplanted tumour in diret contrast to its inhibitory effects in the primary tumours. Several factors may be implicated in these differences between transplanted and DMBA tumours. Firstly, whereas the DMBA tumours are likely to be hormone dependent, the transplanted tumour failed to regress following
I n Vitro Effects of Prolactin
681
Table 1. Metabolism of 7~-3H testosterone by DMBA induced tumours Per cent testosterone metabolised
Rat
A* B]' C* D]. E* Ft
Control + proh, ctin (rat) + growth hormone Control + prolactin (rat) + growth hormone Control + prolactin (rat) + growth hormone Control + prolactin (rat) Control + prolactin (ovine) + growth hormone Control + prolaetin (ovlne) + growth hormone
94-80 85"00 90.20 46.50 35.10 46.10 47.45 43.10 48.20 42-50 37.10 33.85 34.75 31.60 47.80 59.40 44.45
Per cent conversion to 5= DHT
28.50 13.20 24.20 5.50 (-24.5) 3.90 (-0.9) 6.20 16.15 (-9.2) 8.40 (+ 1.6) 13.60 5.05 (-12.6) 2.50 5.65 (+ 2.6) 5.50 - 6.7) 5.00 19.20 +24"3) 9.40 -7.0) 19.40 (-10.3) ( - 4.9)
(-53.6) (-15.1) (-29.1) (+12.7) (-49.0) (-15.8) (-50.5) (-2"7) (-11.5) (-51.1) (-t-1.0)
Per cent conversion to 5= androstanediol 25.40 21.30 22.10 27.05 17-00 26.70 14.15 13.55 17.20 20.10 13.30 12.45 7.60 11.55 11.20 8.75 3.95
Per cent 5= reduction
53.90 34.50 46.30 32.55 (-37.2) 20.90 (-1.3) 32.90 30.30 (-4.2) 21.95 (+21.55) 30.80 25.15 (-33.8) 15.80 18.10 (-39"0) 13.10 ( - 7"2) 16.55 30.40 (-21"9) 18.15 (-64.7) 23.35 (-16.1) (-13.0)
(-36.0) (-14.1) (-35.8) (+ 1.1) (-27.6) (+ 1.7) (-37.2) (-27"6) ( - 8.6) (-40.3) (-23.2)
Figures in parentheses represent the percentage of change caused by addition of prolactin or growth hormone (50/~g/ml). *Intact rat. ]'Rat sequentially oophorectomized and given oestradiol (1 pg daily).
Table 2.
Per cent testosterone metabolised
Rat 1" 2* 3* 4t 5].
Metabolism of 70~-3H testosterone by transplanted tumogrs
Control +prolactin(ovine) Control + prolactin (ovine) Control +prolactin(ovine) Control + prolactin (rat) Control +prolactin(rat)
88"70 95.50 96.80 97.15 98.70 95.50 94.00 97.00 96.70 88.05
Per cent conversion to 5= DHT
19.90 26"50 9"65 (+0.3) 21'90 13"30 ( - 3 " 3 ) 16.50 9.50 (+ 3"I) 24.50 3.40 (-9.0) 5"25
(+7.7)
Per cent conversion to 5~ androstanediol
31.30 (+ 33"2) 59.00 33"60 (+127.0) 30"30 66.15 (+ 24"0) 66.10 39.20 (+158.0) 31.70 50.70 (+ 54.4) 55.10
(+88"5) ( - 9.8) (0) (-19.1) (+ 8.6)
Per cent 5g reduction 51.20 85.50 43.25 52.20 79.45 82.60 48.70 56.20 54.10 60.35
(+67.0) (+20.7) (+ 4.0) (+ 15.4) (+11.6)
*Tumour at 2nd passage. 1"Tumour at 6th passage. Figures in parentheses represent % change caused by addition of prolactin.
o o p h o r e c t o m y ; the effects o f prolactin m a y therefore reflec~ differences between h o r m o n e d e p e n d e n t and. h o r m o n e sensitive tumours. Secondly, there are different circulating prolactin levels in the two strains o f rats u s e d - the A D R A strain, in which the t r a n s p l a n t e d t u m o u r was i n d u c e d a n d subsequently transp l a n t e d , has a lower basal level o f circulating prolactin, in c o m p a r i s o n with the r a n d o m -
b r e d variety in which the p r i m a r y D M B A t u m o u r s were i n d u c e d [4]. A t present, it is not possible to r e m o v e the strain difference as t u m o u r i n d u c t i o n rate b y D M B A in the A D R A r a t is exceptionally low a n d the t r a n s p l a n t e d t u m o u r is not a c c e p t e d b y r a n d o m l y b r e d animals. I n conclusion, it is w o r t h emphasizing t h a t whilst prolactin has a l r e a d y been shown to
682
William R. Miller
affect steroid metabolism in other tissues, such as the prostate [12] and testis [13], its effects in m a m m a r y tumour tissue m a y assume added importance in view of the properties of the 5~ reduced metabolites involved to influence tumour growth.
Acimowledgements--The author thanks Professor A. P. M. Forrest for his interest and encouragement, the Cancer Research Campaign for the Grant to Professor Forrest supporting this work and Miss J. Telford for her technical assistance. Rat and ovine prolactin and rat growth hormone were gifts from the National Institutes of Health (Bethesda, Maryland).
REFERENCES 1.
2. 3.
4.
5. 6. 7. 8.
9. 10. 11. 12.
13.
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