Responsiveness of adenylate cyclase to pituitary gonadotropins and evidence of a hormone-induced desensitization in the lizard ovary.
Gonadotropins (FSH and LH) affect several mammalian gonadal functions. In particular, FSH stimulates oogonial proliferation and oocyte growth, while LH regulates ovulation and progesterone secretion. In lacertilian reptiles, gonadal function is also regulated by pituitary gonadotropins, but which hormone controls ovarian activities and the mechanisms of action are unknown. The present study aimed to clarify mechanisms of action of pituitary gonadotropins on the ovary of Podarcis sicula (Lacertilia). The data demonstrate that mammalian gonadotropins FSH and LH produce a threefold stimulation of adenylate cyclase activity in follicular membranes, while hCG and TSH are less effective, causing a twofold increase in adenylate cyclase activity. Neurotransmitters such as dopamine, serotonin, and catecholamines have no effect on enzyme activity. The action of mammalian FSH and LH on the ovary mimics the effect of homologous hormones: in lizard ovaries incubated in vitro in the presence of isolated homologous pituitary glands, the intracellular cAMP level increased by 50% with respect to control ovaries. Mammalian gonadotropins appear homologous to lizard gonadotropin(s): Southern blot analyses show that the lizard genome contains nucleotide sequences homologous to those encoding for mammalian beta FSH and beta LH. Both homologous and heterologous desensitization of adenylate cyclase activity occurs in the lizard ovary. In fact, responsiveness of adenylate cyclase to gonadotropin stimulation is abolished in animals 2 hr after in vivo treatment with FSH. Sensitivity to gonadotropin stimulation is restored 2 weeks after the beginning of the in vivo treatment. Desensitization was also observed in ovaries incubated in vitro with mammalian FSH or with isolated pituitary glands.
Borrelli
L
L
CNR Institute of Protein Biochemistry and Enzymology, Naples, Italy.
De Stasio
R
R
Bovenzi
V
V
Parisi
E
E
Filosa
S
S
D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D001345:Autoradiography; D015139:Blotting, Southern; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D004247:DNA / Q000032:analysis; D015342:DNA Probes / Q000737:chemistry; D005260:Female; D005300:Fertility Agents, Female / Q000494:pharmacology*; D005640:Follicle Stimulating Hormone / Q000235:genetics / Q000494:pharmacology; D006065:Gonadotropins, Pituitary / Q000494:pharmacology*; D007424:Intracellular Fluid / Q000378:metabolism; D008116:Lizards; D007986:Luteinizing Hormone / Q000235:genetics / Q000494:pharmacology; D008297:Male; D010053:Ovary / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D013737:Testis / Q000378:metabolism
D015342:DNA Probes; D005300:Fertility Agents, Female; D006065:Gonadotropins, Pituitary; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone; D004247:DNA; D000242:Cyclic AMP; D000262:Adenylyl Cyclases