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Daily blood samples from four mares were assayed for cortisol through a total of eight ovulatory cycles. Mean cortisol concentrations on days −14, −13, −10, −9 and −8 before ovulation (dioestrus) were greater than on days −5 to −1 (oestrus). The highest mean (±s.e.m.) value of cortisol occurred on day − 10 (260± 28 nmol/l) and the lowest on day −2 (142 ±14 nmol/l). A single episode on a day in late dioestrus characterized the maximum cortisol value per cycle for five of eight cycles. Extraction of plasma samples with petroleum ether or chromatography before assay, to eliminate interference from progesterone and its metabolites, did not alter the pattern of high dioestrous and low oestrous cortisol concentrations. Maximum follicular diameter at ovulation was negatively correlated with mean cortisol concentration for that cycle. These results indicate that in the mare the adrenals secrete cortisol more actively during dioestrus than during oestrus and suggest that a decline in cortisol values at oestrus may favour full follicular growth and ovulation.
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The use of agarose-bound neurophysin for the extraction of oxytocin from biological fluids is described. Oxytocin can be extracted from plasma, urine and cerebrospinal fluid with a high rate of recovery and samples varying widely in volume and oxytocin concentration can be tested by the method.
Columns can be used to extract and concentrate dilute samples, or to help identify small amounts of neurohypophysial hormones by affinity chromatography. The oxytocin can be eluted from the column directly into the buffer used for subsequent bioassay. The composition of the final extract is constant and independent of the composition of the sample. The specificity of the binding is high. It is suggested that the method has many advantages over others in current use.
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SUMMARY
The changes in plasma ACTH concentration of pregnant sheep and their foetuses during the latter half of pregnancy and during labour were studied. Before 140 days of gestation the mean concentration in foetal arterial plasma was 117 ± 19 (s.e.m.) pg/ml which rose to a mean of 286 ± 63 pg/ml. The rise in ACTH occurred at about the same time as, but not before, the rise in corticosteroid concentration in foetal plasma. The maternal plasma ACTH concentration did not change during the latter half of pregnancy and had a mean concentration of 64 ± 9 pg/ml. During labour there was a progressive rise in the ACTH concentration in foetal plasma which was not associated with any corticosteroid changes. Ethanol did not suppress labour but reduced the ACTH concentration in foetal plasma.
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Departments of Surgery and *Physiology, The Medical School, The University, Newcastle upon Tyne, NE1 7RU
(Received 12 September 1974)
CB 154 lowers plasma prolactin levels in animals (Flückiger, 1972) and in man (Lutterbeck, Pryor, Vangor & Wenner, 1971), in which it has been successfully used to treat galactorrhoea (Besser, Parke, Edwards, Forsyth, & McNeilly, 1972) and to suppress puerperal lactation (Varga, Lutterbeck, Pryor, Wenner, & Erb, 1972). Hyperprolactinaemia occurs in a number of clinical disorders (Horrobin, 1974) and CB 154 may also be used in these conditions. However, the metabolic effects of this potentially useful drug have not been fully investigated in man or in animals.
Twenty male Wistar rats weighing 140–160 g were used. Ten were given 1 mg CB 154 (Sandoz batch No. 193 H3) intraperitoneally at 12.00 h the day preceding the experiment, and a second injection of 1 mg was given at 08.30 h on the
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Lactating guinea-pigs were passively immunized with an antiserum to oxytocin of high titre, specificity and avidity. Single i.v. injections of 0·1–0·4 ml antiserum produced high titres which decayed slowly (half-life ≃7 days). Passively administered antiserum was effective in vivo; the clearance of exogenous oxytocin from plasma was greatly slowed in immunized animals. Passive immunization with 0·4 ml antiserum reduced milk transfer to the litter during suckling episodes of 10 min, and overall litter growth rates were significantly decreased. Non-immune serum was without effect. Plasma neurophysin levels showed the same large rises during suckling in immunized animals, indicating that neurohypophysial activation was unimpaired. Despite the presence of high titres of antiserum, some milk transfer still occurred at milk ejection. In-vitro experiments showed that more than 25% of oxytocin remained free 20 s after mixing with plasma taken from passively immunized animals. It is probable that the antiserum in the circulation was unable to bind all the oxytocin released from the posterior pituitary gland before it reached the mammary gland.
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SUMMARY
Plasma samples from pregnant ewes and their foetuses during the last quarter of gestation were assayed for somatomedin-like activity (SLA) using the porcine costal cartilage assay. In maternal plasma, the mean potency (compared with pooled serum from six sheep) was 0·84 ± 0·05 (s.e.m.) units/ml (n = 15). Somatomedin-like activity in the plasma of five control foetuses (0·91 ± 0·1 units/ml) was similar to the maternal levels and did not change with gestational age. After foetal hypophysectomy the SLA in foetal plasma (0·37 ± 0·05 units/ ml, n = 4) was significantly less than in control animals. In two nephrectomized foetuses, the mean SLA in plasma (0·08 and 0·51 units/ml respectively) was less than in control animals. Retardation of intra-uterine foetal growth was induced by removal of endometrial caruncles before pregnancy in four sheep. The SLA in plasma from these foetuses was 0·38 ± 0·05 units/ml (P< 0·01 v. control animals). The results suggest that SLA in the foetus may be important in the regulation of foetal growth, but they also indicate that factors other than growth hormone may be important in the control of SLA in foetal plasma.
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The release of oxytocin and neurophysin during suckling has been studied in conscious unrestrained guinea-pigs. After prior separation, mothers and litters were allowed to suckle for a period of 10 min, and the weight gain of the litter recorded as an index of milk transfer. Maternal blood samples were obtained without disturbance through previously implanted intravenous cannulae and neurophysin and oxytocin determined on unextracted plasma by specific and sensitive radioimmunoassays. In 82 out of 118 experiments the young gained weight during suckling (1·6±0·1 (s.e.m.) g/pup) and this was associated with large rises in both oxytocin and neurophysin concentrations in plasma (mean concentrations: oxytocin 65·4fmol/ml, neurophysin 360fmol/ml). Where serial samples were taken, oxytocin and neurophysin showed a rapid rise and fall in concentration closely associated with the occurrence of milk ejection as judged by the behaviour of the litter. The present results provide the first direct evidence of a spurt release of both oxytocin and neurophysin measured simultaneously during milk ejection. The conscious lactating guinea-pig thus provides a useful laboratory model in which to study hormone release during milk ejection.
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Abstract
To determine the relationship between placental delivery of oxygen and glucose, circulating insulin-like growth factors (IGFs) and fetal growth, the effect of variable restriction of placental growth was determined in sheep in late gestation. Arterial blood was obtained via indwelling catheters at 120 and 127 days of gestation, prior to necropsy at 130 days to measure fetal and placental weights. Plasma was acidified and subjected to size-exclusion high-performance liquid chromatography at pH 2·8 to dissociate and separate IGFs from their binding proteins. The acid-dissociated IGF fraction was analysed by sensitive and highly specific radioligand assays for IGF-I and IGF-II, previously defined using ovine IGFs. Fetal weight and blood pO2 and glucose at 120 and 127 days of gestation correlated positively with placental weight. Plasma IGF-I was positively associated with fetal weight and fetal liver weight, and with blood pO2 and glucose at both ages. Plasma IGF-II levels also correlated positively with fetal weight, fetal liver weight and with blood glucose and pO2, but only at 127 days of gestation. In the most severely growth-retarded fetal sheep, blood glucose and pO2 and plasma IGF-I were significantly reduced when compared with normal fetuses at 120 days. All decreased further by 127 days of gestation as did plasma IGF-II in severely growth-retarded fetal sheep compared with normal fetuses. These observations are consistent with the hypothesis that both IGF-I and IGF-II are chronically regulated by oxygen and nutrition in utero and mediate part of the influence of placental supply of substrate over fetal growth.
Journal of Endocrinology (1994) 140, 5–13
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SUMMARY
The change in plasma ACTH and corticosteroid concentrations in response to a 60 min period of hypoxaemia were studied in foetal and adult sheep during the latter half of pregnancy. Hypoxaemia consistently caused large rises in the concentration of ACTH in foetal plasma, the magnitude of which did not change with gestational age but was related to the physiological state of the foetus. Before 139 days small and slow rises in corticosteroid (predominantly cortisol) concentration in foetal plasma were observed during hypoxaemia, and these may have been of maternal origin. After 139 days, hypoxaemia caused a rapid and large rise in the concentration of cortisol and corticosterone in foetal plasma, which was largely of foetal origin. Hypoxaemia caused no consistent change in maternal plasma ACTH concentration but was associated with progressive increases in plasma cortisol concentrations. The cortisol:corticosterone ratio in foetal plasma was 1·5 before 139 days and increased to 4·1 several days before term which was lower than the value of 9 in maternal plasma. Small concentrations of 11-deoxycortisol and cortisone were detected in maternal and foetal plasma, the changes of which were small during hypoxaemia.
The results indicate that a maturational change in the sensitivity of the foetal adrenal to endogenous ACTH occurs several days before term.
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SUMMARY
The effect of nephrectomy on the response to thyrocalcitonin was studied in three groups of rats: intact animals on stock diet; parathyroidectomized rats on stock diet; and parathyroidectomized rats on high calcium, low phosphorus diet.
In intact rats and in parathyroidectomized rats on a high calcium, low phosphorus diet, nephrectomy did not alter the fall in plasma calcium and phosphate produced by thyrocalcitonin. In parathyroidectomized rats on stock diet, however, plasma calcium was not changed by the hormone, but there was an isolated fall in phosphate which was prevented by previous nephrectomy.
Experiments with 45Ca showed that when plasma calcium was lowered by thyrocalcitonin this was caused by inhibition of bone resorption.
Since the hormone also causes phosphaturia, it was concluded that there are two sites of action: bone and kidney. The skeletal effect is usually dominant and the renal effect is the major one only when the rate of bone resorption is low.
