CHARACTERIZATION OF THE GONADOTROPIN-SENSITIVE ADENYLATE CYCLASE IN THE CORPUS LUTEUM OF THE RHESUS MONKEY (MACACA MULATTA) DURING THE MENSTRUAL CYCLE.

Abstract

These studies were undertaken to characterize the adenylate cyclase system of the primate (rhesus monkey) corpus luteum, and to correlate gonadotropin-sensitive adenylate cyclase activity with the functional activity of the corpus luteum at specific stages of the luteal phase of the menstrual cycle, particularly near the time of luteolysis. The conversion of [α-³²P] ATP to [³²P] cAMP was assayed in preparations of luteal tissue obtained from rhesus monkeys at midluteal phase of the menstrual cycle. Cyclic AMP production was influenced by the pH, osmolality, and ionic strength of the assay buffer, and was acutely sensitive to Mg⁺². Michaelis-Menten kinetics were seen when the ATP:Mg ratio was constant. The gonadotropins, hLH and hCG but not hFSH, stimulated cAMP production in a similar dose-dependent manner. Deglycosylated hCG blocked the stimulation of adenylate cyclase by hLH and hCG. The addition of GTP increased maximal activation of adenylate cyclase by hLH or hCG but did not alter sensitivity to the hormones. The adenylate cyclase of macaque luteal tissue did not respond to the addition of isoproterenol or epinephrine; furthermore, these catecholamines did not affect hCG-stimulation of adenylate cyclase. Forskolin and fluoride stimulated cAMP production in a dose-dependent manner. The activity of adenylate cyclase was examined in corpora lutea obtained from rhesus monkeys at specific stages in the luteal phase of the menstrual cycle (days 3-5, 6-8, 9-12, 13-15, 16-menses after the midcycle LH surge). Basal adenylate cyclase activity, activity stimulated by GMP-P(NH)P, GTP, GTP + hLH, and GTP + hCG, sensitivity of the enzyme to hLH (measured by K(act)), and peripheral progesterone levels were low in the early luteal phase (days 3-5), increased by midluteal phase (days 6-8 and 9-12), and then decreased by the late luteal phase days 13-15 and 16-menses). In contrast, there were no significant differences among the age groups tested for forskolin-stimulated activity. Thus the adenylate cyclase system of the rhesus monkey undergoes significant changes during the luteal phase which are associated with the development and regression of the corpus luteum of the menstrual cycle. Mechanisms which modulate gonadotropin and nucleotide activation of adenylate cyclase without interfering directly with the catalytic unit are implicated in the changes which accompany luteolysis.