METABOLIC CLEARANCE RATE, PRODUCTION RATE, AND MAMMARY UPTAKE AND METABOLISM OF PROGESTERONE IN COWS R. B.

HEAP, A.

Agricultural

HENVILLE AND J. L. LINZELL Research Council Institute of Animal Physiology, Babraham, Cambridge, CB2 4AT

(Received

16 October

1974)

SUMMARY

Tracer kinetic techniques have been used to measure the production rate, metabolic clearance rate and mammary uptake of progesterone in six experiments on two Jersey cows. The cows were surgically prepared so that the carotid artery, jugular vein and mammary vein concentrations of progesterone, and udder blood flow, could be determined in conscious animals without anaesthesia or stress. The mean production rate of progesterone was 173 \m=+-\23\m=.\3(s.e.m.) \g=m\g/min, with values ranging from 80 to 276 \g=m\g/min in pregnancy. The metabolic clearance rate was 22\m=.\5\m=+-\ 2\m=.\01/min, or 0\m=.\21\m=+-\0\m=.\0251/min/kg metabolic body weight. The mammary uptake of progesterone was low, 3\m=.\1\m=+-\1\m=.\1\g=m\g/min, and udder uptake accounted for about 3 % of

progesterone production

rate.

During [3H]progesterone infusion, radioactivity was transferred from blood to milk, probably by diffusion down a concentration gradient. Progesterone accounted for more than 88 % of the ether-soluble radioactivity recovered from milk. introduction

Progesterone and related steroids have been identified and estimated in cows' milk (McCracken, 1963; Laing & Heap, 1971; Darling, Kelly, Laing & Harkness, 1972; Heap, Gwyn, Laing & Walters, 1973; Darling, Laing & Harkness, 1974) but it is not known whether their occurrence in milk is due to mammary extraction and metabolism, which is appreciable in the goat (Heap & Linzell, 1966; Heap, Linzell & Slotin, 1969; Heap, Bedford & Linzell, 1975), or to diffusion down a concentration gradient owing to the high lipid solubility of progesterone in milk fat (Heap, Symons & Watkins, 1970). In the event that milk progesterone measurements can be used for pregnancy diagnosis (Laing & Heap, 1971; Heap et al. 1973; Heap & Laing, 1974) and applied clinically in the diagnosis of basic information is also needed about the kinetics of progesterone metabolism in the cow, together with measurements of the mammary uptake of progesterone and the rate of transfer of the hormone across the mammary gland into milk, which previously has been studied only in dairy goats (Heap & Linzell, 1966; Linzell & Heap, 1968).

infertility,

MATERIALS AND METHODS

Cows Two Jersey cows were used which had been surgically prepared with an exteriorized carotid artery and superficial epigastric vein (mammary or 'milk' vein) which, by removing minor

veins that cross the mid-line between the two halves of the udder, drained only one half of the udder. A few hours before an experiment catheters were placed in the exteriorized carotid artery and a jugular vein by the method of Seldinger (1953). The experiments were carried out in conscious animals in the milking parlour next to the laboratory. The cows were 4 years old at the start of the investigation, and R16 (Beauty) and R23 (Ruby) had completed three and two normal pregnancies respectively.

Progesterone infusion similar to that described by Bedford, Harrison & Heap experimental procedure (1972). [7a-3H]Progesterone (1 mCi) (6-1 Ci/mmol, The Radiochemical Centre, Amersham) dissolved in 50 ml 2 % ethanol : sterile saline (154 mM-NaCl) was infused at a constant rate through a PTFE catheter (1-0 mm internal diameter 1-6 mm outer diameter) into a The

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Metabolic clearance rate, production rate, and mammary uptake and metabolism of progesterone in cows.

Tracer kinetic techniques have been used to measure the production rate, metabolic clearance rate and mammary uptake of progesterone in six experiment...
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