Metabolic Clearance Rate, Production Rate and Mammary Uptake of Progesterone in the Goat

Abstract

The dynamics of progesterone uptake and metabolism in the mammary gland of the goat have been measured and related to the metabolic clearance rate and production rate of the hormone determined by tracer kinetic techniques. The metabolic clearance rate of progesterone from blood was 3-13 plus or minus 0-35 (S.E.M.) 1/min in ten experiments on six goats; values tended to be slightly higher in pregnant than in non-pregnant goats. The production rate of progesterone at oestrus, and at day 3 of the normal cycle, was less than 0-01 mug/min. During the luteal phase of the oestrous cycle the production rate was 8-5 and 14-6 mug/min in 2 animals, and in the second half of pregnancy, 15-3 plus or minus 0-6 mug/min (5 animals). Progesterone was extracted from the circulation by the mammary gland of conscious goats with an efficiency of 49-4 plus or minus 11-3% in non-pregnant, and 51-7 plus or minus 11-5% in pregnant aniamals. The mean clearance rate of progesterone by the udder was 0-279 1/min, 8-8% of the metabolic clearance rate. Mammary uptake of progesterone in goats with an actively secreting corpus luteum was 0-64 plus or minus 0-29 mug/min, which gave an estimated value of 0-11-1-88 ng/min/g mammary gland. The mammary extraction of progesterone was investigated in a goat 3 days after oestrus when any high affinity receptor sites would presumably be unoccupied. During the infusion of progesterone into a mammary artery, tissue sample were taken from various organs, including the mammary gland, and the concentration of labelled compounds at steady state was determined. A high mammary extraction of progesterone was found to be determined. A high mammary extraction of progesterone was found to be attributable principally to progesterone metabolism. The metabolites of progesterone were removed from the gland in venous blood and were not stored to any appreciable extent in mammary tissue. Experiments in vitro confirmed the findings in vivo that mammary tissue metabolized labelled progesterone and also pregnenolone and androstenedione; metabolism of dehydroepiandrosterone, oestradiol-17 beta, oestrone and cortisol was relatively small. Confirmation of our previous finding that the mammary gland of the goat can synthesize progesterone from labelled pregnenolone infused into the gland in vivo, further implicated this organ as an active site of metabolism of certain steroids. The physiological role of steroid metabolism in the mammary gland is discussed.

Mammary Growth During Pregnancy in Hypophysectomized or Bromocriptine-Treated Goats

“…Goats, however, do not secrete progesterone from their placentae, and the pregnancy has to be maintained after hypophysectomy by injections of gonado¬ trophin or progesterone (Buttle, 1978). In the present study, injections of 20 mg progesterone/ day for 60 days satisfactorily replaced the endogenous progesterone produced by the ovaries and resulted in the peripheral concentrations being only slightly below the normal range; this dosage is in good agreement with an estimated progesterone production of 22 mg/day in normal goats during late pregnancy (Heap, Bedford & Linzell, 1975).…”

Excretion rate of progesterone in milk and faeces in lactating dairy cows with two levels of milk yield

“…I). These data and other findings [5,8,9] suggest that the metabolic role of the mammary gland is not great and that milk P4 concentration may have been influenced by milk fat content and also the body mass.…”

Metabolic Clearance Rate, Production Rate, and Mammary Uptake and Metabolism of Progesterone in Cows

“…Values for the metabolic clearance rate (MCR) of progesterone from blood, its production rate (PR) and mammary extraction were calculated as described by Bedford et al (1972) and Heap et al (1975). The blood concentration of endogenous progesterone was estimated from the plasma concentration which was corrected for the procedural losses during extrac¬ tion (10 %), the haematocrit, and the amount of progesterone associated with erythrocytes (10%).…”