SUMMARY A competitive protein-binding assay of progesterone and a radioimmunoassay of total unconjugated oestrogens were evaluated and employed in the measurement of these steroids in the plasma of guinea-pigs at different times during the reproductive cycle. Production rates (PR) were calculated from the product of the endogenous steroid concentration and its metabolic clearance rate. During the oestrous cycle, plasma progesterone levels rose from undetectable levels at the time of ovulation to 2·8 ± 0·33 (s.e.m.) ng/ml 5 days later; PR was 0·26 mg/day. During pregnancy, plasma progesterone concentrations in post-partum mated guinea-pigs rose from 15 ng/ml at day 15 post coitum (p.c.) (PR, 0·65 mg/day) to a peak value of 329 ± 14 ng/ml by days 30 to 45. The concentration fell 51–55 days p.c. (160 ± 14·7 ng/ml), but rose before parturition to 258 ± 22 ng/ml. After day 20 p.c., PR was 1·24 ± 0·3 mg/day. After parturition, plasma progesterone levels fell rapidly and during lactation were about 10 ng/ml (PR, 0·4 mg/day). Total unconjugated oestrogens in arterial plasma were not detected in early pregnancy, but rose from values of 12·8 ± 1·9 pg/ml (days 31–35) to 31·0 ± 5·2 pg/ml (days 56–60). There was a slight fall before, and a rapid one after parturition. The ratio of progesterone to oestrogen in plasma fell during pregnancy and reached its lowest values between days 55 and 60.

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The close-arterial infusion of free insulin-like growth factor-I (IGF-I; 1.1 nmol/min) for 6 h into the pudic artery supplying one mammary gland of lactating goats caused a 25 +/- 6% (mean +/- S.E.M., n = 6) increase in the rate of milk secretion of that gland. The increase in the rate of milk secretion in the adjacent noninfused gland (14 +/- 4%) was not significantly different from that observed during saline infusion (4 +/- 5%). Blood flow to the infused gland was increased from 378 +/- 26 ml/min 1 h before to 487 +/- 56 ml/min approximately 5 h after the start of the infusion of IGF-I, declining to 420 +/- 44 ml/min approximately 2 h after the end of the infusion. The total concentration of IGF-I (free and bound) in milk of the infused gland was significantly higher than that of the non-infused gland. The concentrations of IGF-I in carotid arterial plasma samples increased during IGF-I infusion from a mean value of 32 +/- 2 nmol/l before to a maximum of 49 +/- 3 nmol/l 5 h after the infusion commenced. Circulating concentrations of total IGF-I declined slowly after the infusion with an estimated half-life of 5 h. Infusion of saline alone did not alter mammary blood flow or the concentration of total IGF-I in milk or plasma. The results indicate that the infusion of free IGF-I into the mammary arterial supply enhances milk secretion and mammary blood flow in intact, conscious goats.(ABSTRACT TRUNCATED AT 250 WORDS)

Steroid hormone concentrations in plasma have been measured in blood samples taken from conscious sows with ear vein catheters. In late pregnancy, the plasma progesterone concentration ranged from 6 to 12 ng/ml and it decreased in all animals before the onset of parturition. Total unconjugated oestrogens increased to high values of up to about 3 ng/ml in late pregnancy and then declined after the onset of parturition. Oestrone was the predominant unconjugated oestrogen measured. Plasma corticosteroid (mainly cortisol) concentration was about 33 ng/ml and showed no consistent change at the time of parturition. During lactational anoestrum the plasma concentration of progesterone and total unconjugated oestrogens was very low, while that of corticosteroids was 21 ng/ml. When the piglets were weaned at 26-31 days, sows came into oestrus 4-12 days later, and this was preceded, or accompanied by, an increase in plasma oestrogens. In the luteal phase, plasma progesterone concentrations rose to 20-35 ng/ml. A sow whose piglets were removed at birth, showed signs of oestrus (vulval enlargement and a lordosis response), but a lack of receptivity to the boar associated with no detectable changes in the plasma oestrogen concentration; however, ovulation probably occurred since plasma progesterone values increased in a manner comparable to that found after the formation of normal corpora lutea in other sows. After a second non-receptive cycle, the sow was mated and became pregnant at the third post-weaning oestrus. At parturition the concentration of progesterone and total unconjugated oestrogens was greater in placental venous plasma than in maternal jugular plasma, which indicates placental synthesis of these hormones. A greater concentration of plasma corticosteroids in foetal blood than in placental venous or maternal jugular plasma suggests foetal synthesis in late pregnancy.

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In 12 anaesthetized boars the concentrations of oestrone sulphate and dehydroepiandrosterone sulphate (DHAS) were 15- to 35-fold higher in lymph collected from a vessel in the spermatic cord than in testicular venous blood plasma from a vein in the spermatic cord. The concentrations of testosterone, total unconjugated oestrogens and dehydroepiandrosterone (DHA) were about twofold higher in lymph. The concentrations of all steroids studied were higher in testicular venous blood plasma than in arterial blood plasma (testosterone about sixfold; total unconjugated oestrogens about fourfold; oestrone sulphate about threefold; DHA and DHAS about twofold), but the concentrations of testosterone, total unconjugated oestrogens and oestrone sulphate in rete testis fluid were comparable to those in arterial blood plasma. Lymph flow from the pig testis was about 7% of plasma flow so that about 80% of the oestrone sulphate and DHAS produced by the testis leaves the organ in the lymph; the comparable values for testosterone, total unconjugated oestrogen and DHA were about 20%. In the 90-min period following an injection of human chorionic gonadotrophin there were substantial increases in the concentration of testosterone and smaller increases in the other steroids in arterial and spermatic venous blood plasma and in testicular lymph, but not in rete testis fluid; there were also small increases in lymph flow, but no change in blood flow.

SUMMARY Tracer kinetic techniques were used to determine the metabolic clearance rate (MCR) and production rate (PR) of progesterone in the sheep during pregnancy, the oestrous cycle and the lactation anoestrus. The MCR from whole blood measured by the continuous infusion of [3H]progesterone was 3·483 ± 0·126 l/min in pregnancy, 2·752 ± 0·239 l/min in the oestrous cycle and 5·020 ± 0·566 l/min in lactation anoestrus. After correcting for body weight the respective values were 0·077, 0·077 and 0·133 l/min/kg. The PR ranged from 0·60 to 6·75 μ/min in the oestrous cycle and 6·66 to 72·14 μg/min in pregnancy. In the last 4 weeks of gestation the PR of progesterone was significantly greater in ewes bearing foetuses with birth weights of more than 4 kg than in ewes with smaller lambs. The conversion or isotope concentration ratio of progesterone to 20α hydroxypregn-4-en-3-one (20α-diHP) was 69·4±10·0% in non-pregnant and 77·2 ± 4·8% in pregnant sheep. The concentrations of [3H]progesterone and [3H]20α-diHP were closely correlated. There was an appreciable extraction (25·4 ± 3·0%) of progesterone and production (9·1 ± 2·0% of 20α-diHP by the head.