EFFECT OF PROSTAGLANDIN
E2
ON THE CONCENTRATION OF
CORTISOL IN THE PLASMA OF NEWBORN LAMBS J. R. G. CHALLIS, G. D. CARSON AND F. NAFTOLIN McGlll University, Department of Obstetrics and Gynecology, Royal Victoria Hospital, Women's Pavilion, Montreal, Quebec H3A 1A1, Canada
(Received 26 July 1977) Infusion of prostaglandin E2 (PGE2) into the carotid artery of the foetal lamb increases the concentration of cortisol in the foetal plasma (Louis, Challis, Robinson & Thorburn, 1976) even at stages of pregancy when the foetal adrenal gland is relatively insensitive to endogenous or exogenous adrenocorticotrophin (ACTH; Bassett & Thorburn, 1973; Boddy, Jones, Mantell, Ratcliffe & Robinson, 1974). We have now examined the site of this prostaglandin action in lambs aged 5\p=n-\6days, by which time closure of the ductus arteriosus is advanced (see Dawes, 1968), and pulmonary metabolism should separate the effects of prostaglandins administered into the brachiocephalic trunk or descending aorta. The lambs used in this study were born spontaneously at full term. They were housed with their mothers except during experimental periods. Vascular catheterization with a number 3F umbilical artery catheter (Sherwood Industries, St Louis, Missouri) was performed under local anaesthesia (1% xylocaine, Astra Pharmaceuticals) in three groups of lambs at 3-4 days of age at least 48 h before the experiment began. In group I (four lambs) a catheter was introduced into the lower abdominal aorta via the femoral artery. In group II (six lambs) a catheter was introduced into the median artery and advanced until its tip lay in the brachiocephalic trunk. In group III (five lambs) one catheter was positioned in the brachiocephalic trunk and a second catheter, introduced into the femoral artery, was advanced so that its tip lay in the thoracic aorta at the level of the seventh thoracic vertebra. The position of the catheters was established by X-ray at the time of the operation and again after experimentation. The catheters were then filled with heparin-saline (1000 u./ml). The direction of flow was ascertained by injecting 10 ml contrast medium (Renografin, Squibb). Studies were performed between 08.30 and 12.00 h in an isolated laboratory and with the lambs gently restrained in a canvas sling. After an acclimatization period of 30 min, three control samples were taken at 15 min intervals. Immediately after the third sample, test substances were injected as follows: group I, 100 µg ACTH (Synacthen, ACTH^^, Ciba); group II, initially saline-treated controls, then using an identical procedure, 50 µg PGE2 (Upjohn Co.) were injected 24 h later; group III, 50µg PGE2 into the thoracic aorta. Injections were made in 1 ml saline over a period of 15 s and flushed in with 2 ml saline. Blood samples (1 ml) were collected at the time intervals indicated in Table 1. Plasma was obtained and the concentration of cortisol determined by radioimmunoassay as described previously (Louis et al. 1976). The interassay coefficient of variation was about 12%. There was no significant difference (P>0-05, i-test) between the concentrations of cortisol in the plasma of group II and III lambs before injection of PGE2 (Table 1). Injection of
Synacthen (group I) or PGE2 into the brachiocephalic artery (group II) produced a sig¬ nificant increase in the concentration of cortisol in the plasma (P0-05) in the concentration of cortisol in the plasma after injection of PGE2 into the thoracic aorta above the arterial supply to the adrenal glands, which arises at the level of the first lumbar vertebra.
Table 1. Concentration of cortisol in the plasma of newborn lambs at various times before and after injection of ACTH (Synacthen) or prostaglandin E% (PGE2) (means ± s.e.m.) Plasma cortisol (ng/ml) Test
Groupf substance I Synacthen Saline
II II
PGEj
III
PGEa
—30 min —15 min 0 min 13-7 27-4 16-8
15 min 82-5*
30 min 92-5*
45 min 104-0*
60 min 102-6*
90 min 120 min 102-6* 62-5
±14-3
±60-7
±3-7
±2-8
±21-4
±16-8
±14-5
±17-7
±51-9
39-2
28-5
35-3
35-3
28-1
39-6
38-2
34-8
±11-0
±16-9
±15-7
±19-7
±6-4
±19-8
±15-1
±23-5
±7-9
±27-9
±22-1
33-2
28-4
23-2
±7-4
±5-4
±5-5
35-8 44-8
±15-6 26-1
±9-5
31-0
±15-3 29-6
±5-6
26-7
±7-1 32-9
±5-7
97-2*
±9-9 28-4
±6-7
106-5*
±7-5
72-8*
77-6*
64-2*
±11-2 21-6
±8-7
78-3
±21-6 28-3
±7-6
Significantly greater (P< 0-001) than the average control (pre-injection) value for that group. t For details of catheter placement and injection schedules, see text. *
This study shows that PGE2 will stimulate an increase in the concentration of cortisol in the plasma of newborn lambs, as in the foetus (Louis et al. 1976). However, PGE2 does not appear to act directly on the adrenal gland, but indirectly, mediated via the brain and/or the pituitary gland. Adrenocorticotrophin may have been released in the present study, but if the pituitary gland and/or brain is the site of PGE2 action in the foetus, the effect on the level of cortisol is unlikely to be due to ACTH because it is seen at a stage of pregnancy when the foetal adrenal gland is relatively insensitive to ACTH. This suggests the possible release of, and trophic role for, other messengers of intracranial origin during foetal life (Silman, Chard, Lowry, Smith & Young, 1976).
We thank Ms J. Mannard, Mrs L. Carter and Mr P. Ferraro for their technical assistance. This work was supported by the Fraser Memorial Trust of the Royal Victoria Hospital, the Quebec Research Council and Medical Research Council Grant MA-6070 and MT-5823. J.R.G.C. is a Canada MRC Scholar. REFERENCES In D. G. Bassett, J. M. & Thorburn, (1973). Endocrinology ofpregnancy and parturition: experimental studies in sheep, pp. 126-140. Ed. C. G. Pierrepoint. Cardiff: Alpha Omega Alpha. Boddy, K, Jones, C. T., Mantell, C, Ratcliffe, J. G. & Robinson, J. S. (1974). Endocrinology 94, 588-591. Dawes, G. S. (1968). Foetal and neonatal physiology. Chicago: Year Book Medical Publishers. Louis, T. M., Challis, J. R. G., Robinson, J. S. & Thorburn, G. D. (1976). Nature 264, 797-798. Silman, R. E., Chard, T., Lowry, P. J., Smith, I. & Young, I. M. (1976). Nature 260, 716-718.
E2
ON THE CONCENTRATION OF
CORTISOL IN THE PLASMA OF NEWBORN LAMBS J. R. G. CHALLIS, G. D. CARSON AND F. NAFTOLIN McGlll University, Department of Obstetrics and Gynecology, Royal Victoria Hospital, Women's Pavilion, Montreal, Quebec H3A 1A1, Canada
(Received 26 July 1977) Infusion of prostaglandin E2 (PGE2) into the carotid artery of the foetal lamb increases the concentration of cortisol in the foetal plasma (Louis, Challis, Robinson & Thorburn, 1976) even at stages of pregancy when the foetal adrenal gland is relatively insensitive to endogenous or exogenous adrenocorticotrophin (ACTH; Bassett & Thorburn, 1973; Boddy, Jones, Mantell, Ratcliffe & Robinson, 1974). We have now examined the site of this prostaglandin action in lambs aged 5\p=n-\6days, by which time closure of the ductus arteriosus is advanced (see Dawes, 1968), and pulmonary metabolism should separate the effects of prostaglandins administered into the brachiocephalic trunk or descending aorta. The lambs used in this study were born spontaneously at full term. They were housed with their mothers except during experimental periods. Vascular catheterization with a number 3F umbilical artery catheter (Sherwood Industries, St Louis, Missouri) was performed under local anaesthesia (1% xylocaine, Astra Pharmaceuticals) in three groups of lambs at 3-4 days of age at least 48 h before the experiment began. In group I (four lambs) a catheter was introduced into the lower abdominal aorta via the femoral artery. In group II (six lambs) a catheter was introduced into the median artery and advanced until its tip lay in the brachiocephalic trunk. In group III (five lambs) one catheter was positioned in the brachiocephalic trunk and a second catheter, introduced into the femoral artery, was advanced so that its tip lay in the thoracic aorta at the level of the seventh thoracic vertebra. The position of the catheters was established by X-ray at the time of the operation and again after experimentation. The catheters were then filled with heparin-saline (1000 u./ml). The direction of flow was ascertained by injecting 10 ml contrast medium (Renografin, Squibb). Studies were performed between 08.30 and 12.00 h in an isolated laboratory and with the lambs gently restrained in a canvas sling. After an acclimatization period of 30 min, three control samples were taken at 15 min intervals. Immediately after the third sample, test substances were injected as follows: group I, 100 µg ACTH (Synacthen, ACTH^^, Ciba); group II, initially saline-treated controls, then using an identical procedure, 50 µg PGE2 (Upjohn Co.) were injected 24 h later; group III, 50µg PGE2 into the thoracic aorta. Injections were made in 1 ml saline over a period of 15 s and flushed in with 2 ml saline. Blood samples (1 ml) were collected at the time intervals indicated in Table 1. Plasma was obtained and the concentration of cortisol determined by radioimmunoassay as described previously (Louis et al. 1976). The interassay coefficient of variation was about 12%. There was no significant difference (P>0-05, i-test) between the concentrations of cortisol in the plasma of group II and III lambs before injection of PGE2 (Table 1). Injection of
Synacthen (group I) or PGE2 into the brachiocephalic artery (group II) produced a sig¬ nificant increase in the concentration of cortisol in the plasma (P0-05) in the concentration of cortisol in the plasma after injection of PGE2 into the thoracic aorta above the arterial supply to the adrenal glands, which arises at the level of the first lumbar vertebra.
Table 1. Concentration of cortisol in the plasma of newborn lambs at various times before and after injection of ACTH (Synacthen) or prostaglandin E% (PGE2) (means ± s.e.m.) Plasma cortisol (ng/ml) Test
Groupf substance I Synacthen Saline
II II
PGEj
III
PGEa
—30 min —15 min 0 min 13-7 27-4 16-8
15 min 82-5*
30 min 92-5*
45 min 104-0*
60 min 102-6*
90 min 120 min 102-6* 62-5
±14-3
±60-7
±3-7
±2-8
±21-4
±16-8
±14-5
±17-7
±51-9
39-2
28-5
35-3
35-3
28-1
39-6
38-2
34-8
±11-0
±16-9
±15-7
±19-7
±6-4
±19-8
±15-1
±23-5
±7-9
±27-9
±22-1
33-2
28-4
23-2
±7-4
±5-4
±5-5
35-8 44-8
±15-6 26-1
±9-5
31-0
±15-3 29-6
±5-6
26-7
±7-1 32-9
±5-7
97-2*
±9-9 28-4
±6-7
106-5*
±7-5
72-8*
77-6*
64-2*
±11-2 21-6
±8-7
78-3
±21-6 28-3
±7-6
Significantly greater (P< 0-001) than the average control (pre-injection) value for that group. t For details of catheter placement and injection schedules, see text. *
This study shows that PGE2 will stimulate an increase in the concentration of cortisol in the plasma of newborn lambs, as in the foetus (Louis et al. 1976). However, PGE2 does not appear to act directly on the adrenal gland, but indirectly, mediated via the brain and/or the pituitary gland. Adrenocorticotrophin may have been released in the present study, but if the pituitary gland and/or brain is the site of PGE2 action in the foetus, the effect on the level of cortisol is unlikely to be due to ACTH because it is seen at a stage of pregnancy when the foetal adrenal gland is relatively insensitive to ACTH. This suggests the possible release of, and trophic role for, other messengers of intracranial origin during foetal life (Silman, Chard, Lowry, Smith & Young, 1976).
We thank Ms J. Mannard, Mrs L. Carter and Mr P. Ferraro for their technical assistance. This work was supported by the Fraser Memorial Trust of the Royal Victoria Hospital, the Quebec Research Council and Medical Research Council Grant MA-6070 and MT-5823. J.R.G.C. is a Canada MRC Scholar. REFERENCES In D. G. Bassett, J. M. & Thorburn, (1973). Endocrinology ofpregnancy and parturition: experimental studies in sheep, pp. 126-140. Ed. C. G. Pierrepoint. Cardiff: Alpha Omega Alpha. Boddy, K, Jones, C. T., Mantell, C, Ratcliffe, J. G. & Robinson, J. S. (1974). Endocrinology 94, 588-591. Dawes, G. S. (1968). Foetal and neonatal physiology. Chicago: Year Book Medical Publishers. Louis, T. M., Challis, J. R. G., Robinson, J. S. & Thorburn, G. D. (1976). Nature 264, 797-798. Silman, R. E., Chard, T., Lowry, P. J., Smith, I. & Young, I. M. (1976). Nature 260, 716-718.
