Human chorionic gonadotropin-induced heterologous desensitization of adenylyl cyclase from highly luteinized rat ovaries: attenuation of regulatory N component activity.

We injected hCG into superovulated rats on the seventh day of pseudopregnancy and confirmed previous findings that this results in both homologous desensitization of luteal adenylyl cyclase (loss of responsiveness to LH) and heterologous desensitization of the same adenylyl cyclase system (partial loss of responsiveness to catecholamines), and that these changes are associated with the loss of available unoccupied LH receptors (down-regulation) but not with any discernible loss of beta-adrenergic receptors. We tested the hypothesis that the heterologous component of the above changes might be due to alterations in the function of the nucleotide-binding N component of adenylyl cyclase that intervenes between receptors and catalytic units of adenylyl cyclase. This was done by assessing N component activity in reconstitution assays that measured the capacity of luteal N to mediate, in cyc- S49 lymphoma membranes, stimulation of adenylyl cyclase independently by the guanine nucleotide guanylyl imidodiphosphate, by NaF, or by the lymphoma membrane beta-adrenergic receptor. By all of these modes of assay, heterologous desensitization of luteal adenylyl cyclase to beta-adrenergic stimulation was found to be associated with a proportionally similar decrease in N component activity. This change in N component activity could be due to either quantitative or qualitative alterations. It is speculated that if the change is of a qualitative nature, the alteration may be a cAMP-dependent phosphorylation reaction of one of the subunits of the N component.