Arterial concentration, ovarian secretion and mammary uptake of progesterone in goats during the reproductive cycle.

Abstract

SUMMARY Plasma progesterone concentration was measured in arterial, jugular, mammary venous and ovarian venous blood of 20 goats, together with measurements of mammary and ovarian blood flow. The level in arterial plasma in conscious normal and in castrated males was less than 2·6 ng./ml.; in anoestrous and oestrous females it was 3·4 ± 0·8 (s.e.) ng./ml. In the luteal phase of the ovarian cycle the level rose to 10·7 ± 2·2 ng./ml. and during pregnancy it remained above 10 ng./ml. until near term. In a goat that aborted at 15 weeks of pregnancy no progesterone was detected 3 days before or at the time of abortion. When an active corpus luteum was present in the ovaries, the mammary venous level of progesterone was lower than the arterial concentration in 38 out of 44 instances, the mean difference being 23 ± 4% of the arterial level. In two goats the concentration in jugular vein blood was 80 and 85% of the arterial level but the mammary venous levels were lower still (57 and 75 % of the arterial concentration, respectively). In three goats sampled repeatedly during the whole reproductive cycle, simultaneous measurement of mammary blood flow showed that during pregnancy the udder was taking up to 2–30 ng. progesterone/min./10 g. tissue from the plasma. In a fourth, much older goat (in early pregnancy, but not lactating), the uptake was consistently lower. In all four animals the arteriovenous difference was linearly related to the arterial plasma concentration (r = 0·84). In ovarian venous blood, collected under spinal anaesthesia, the plasma concentration was not significantly different from that in peripheral blood during anoestrus and oestrus, but when active corpora lutea were present the concentration was 620–1600 ng./ml. Simultaneous measurement of ovarian venous outflow suggested that 9–10·5 mg. progesterone/day was being produced by the ovaries, and about 20 % of this was taken up by the udder. Peripheral blood progesterone levels were unaffected by chasing the animal but were raised by spinal anaesthesia and were raised still further after laparotomy.