The stimulatory effect of luteinizing hormone on adenyl cyclase in the bovine corpus luteum.

Adenyl cyclase and cyclic 3’,5’-nucleotide phosphodiesterase were shown in homogenates of bovine corpora lutea. In order to determine the site of action of luteinizing hormone, the adenyl cyclase activity was assessed in the absence of phosphodiesterase activity. This was accomplished by using a high concentration of theophylline and short incubation periods. Under these conditions, luteinizing hormone signilicantly increased the adenyl cyclase activity. NaF produced an even more marked stimulation of this enzyme. Epinephrine at a concentration of 0.2 mM produced a small but statistically significant stimulation of adenyl cyclase, but preparations of luteinizing hormone inactivated by hydrogen peroxide, bovine serum albumin, prolactin, adrenocorticotropin, and glucagon were inert in homogenates that responded to luteinizing hormone and NaF. The minimum effective dose of luteinizing hormone was 0.1 pg per ml. Luteinizing hormone had no effect on the phosphodiesterase activity when assayed under a variety of conditions, but NaF produced a slight but significant inhibition of this enzyme activity when the substrate cyclic AMP was added at a saturating level. These data indicate that the increase in endogenous cyclic AMP brought about by luteinizing hormone is due to a stimulation of the adenyl cyclase rather than to an inhibition of the phosphodiesterase.