Decrease of various luteal enzyme activities during prostaglandin F2 alpha-induced luteal regression in bovine.

Luteal gonadotropin receptors decrease in cows, sheep and rats within 24 h following an injection of a luteolytic dose of prostaglandin (PG) F2 alpha. But it is not known whether this decrease is the specific event, or a reflection of general decline in luteal cell structure, function and metabolism. In order to investigate this possibility, 15 of 21 heifers were given on day 9 of the estrous cycle, a single 500 micrograms injection of Cloprostenol (CO), a synthetic PGF2 alpha analog. These heifers were ovariectomized in groups of 5 at 12, 24 and 36 h after CO. For controls, a group of 6 heifers were ovariectomized just prior to injection of the others. Serum progesterone levels decreased whereas LH levels increased (P less than 0.05) by 12 h with no additional changes observed at 24 or 36 h. The luteal plasma membranes [125I]hCG specific binding, as well as 5'-nucleotidase (5'-NE) activity, decreased by 12 h and continued to decline (P less than 0.05) until 24 h (binding) or 36 h (5'-NE). Scatchard analysis showed that the decrease in [125I]hCG binding was due to a decrease in receptor number rather than a decrease in receptor affinity. The activities of cytochrome c oxidase in mitochondria, NADH cytochrome c reductase in rough endoplasmic reticulum and galactosyl transferase in Golgi decreased while NAD pyrophosphorylase in nuclei virtually disappeared following the injection of CO. The beta-N-acetyl-D-glucosaminidase (a lysosomal hydrolase) activity in the homogenate increased by 12 h and continued to increase up to 36 h.(ABSTRACT TRUNCATED AT 250 WORDS)