Purine amplification of luteinizing hormone action in ovarian luteal cells.

Adenosine produced a severalfold amplification of luteinizing hormone (LH)-stimulated cAMP accumulation and progesterone secretion in rat luteal cells, but showed no similar effect on LH-stimulated cAMP accumulation and androgen secretion in Leydig cells. In the absence of LH, adenosine produced a small but significant stimulation of cAMP accumulation and steroid secretion in both luteal and Leydig cells. In isolated luteal membranes, adenosine increased LH-stimulated adenylate cyclase activity, but this response was small compared to the effect seen in intact cells. The ED60 of adenosine for amplification of LH-stimulated cAMP accumulation in luteal cells was 22 p ~ ; deoxycoformycin, an inhibitor of adenosine deaminase, increased adenosine potency (EDso 10 p ~ ) and treatment with adenosine deaminase decreased maximum adenosine activity by 25%. ATP, ADP, and AMP were equipotent with adenosine; inosine and adenine showed 75 and 30%, respectively, of the maximum activity of adenosine. Adenosine deaminase treatment reduced activity of ATP, ADP, AMP, and adenosine to a level similar to that of inosine but had no effect on the activity seen with inosine or adenine. It was concluded that the activity of the adenine nucleotides was probably due to adenosine formation. The relative potency of the adenine-derived purines was adenosine > inosine > adenine. Guanosine, guanine, cytidine, cytosine, thymidine, and thymine were inactive. None of the purines inhibited LH-stimulated cAMP accumulation, LH receptor binding activity, or progesterone secretion. An adenosine analog, 2-chloroadenosine, which is resistant to metabolism, mimicked the effect of adenosine but with 80% less activity. Dipyridamole, a drug which inhibits cellular transport of purines, inhibited luteal cell uptake of adenosine (ICso 5 PM) and amplification of LH-stimulated cAMP accumulation produced by adenosine (I& 3 ELM). Maximal inhibition of this effect of adenosine by dipyridamole was about 75%. Dipyridamole had no effect on 2-chloroadenosine-dependent amplification of LH-stimulated cAMP accumulation, but completely blocked the response to inosine. Theophylline also inhibited both cellular uptake of adenosine 7 mM) and adenosine amplification of CAMP accumulation. It is suggested that a major component (-80%) of amplification by adenosine of LH-stimulated cAMP accumulation is dependent on cellular transport of the purine, a conclusion based on inhibition of uptake of adenosine by dipyridamole and theophylline. Since