title: Adenylyl cyclase responsiveness to guanyl nucleotides in the developing rat heart.
abstract: Guanyl nucleotides are effective activators of rat heart adenylyl cyclase activity from the earliest age studied, 16 fetal days, through adulthood. Both guanosine triphosphate and guanylyl-imidodiphosphate (GMP-PNP) significantly enhance epinephrine-stimulated adenylyl cyclase activity at all fetal and postnatal ages. The dose-response curves for epinephrine alone, GMP-PNP alone, or for the combination of epinephrine and GMP-PNP are similar for the newborn and adult heart preparations. Our results indicate that the epinephrine-guanyl nucleotide-adenylyl cyclase system is "mature" as a functional unit in the rat heart even prior to birth. The rat heart adenylyl cyclase system shows a dramatic increase in responsiveness to epinephrine and to guanyl nucleotides just before birth, a responsiveness which rapidly falls by 3 days of neonatal life. With increasing age, the absolute guanosine triphosphate or GMP-PNP activated rate rises in parallel with the basal rate of adenylyl cyclase activity in the rat heart. Speculation. The activation of adenylyl cyclalse systems by guanyl nucleotides may be a general feature of fetal as well as of adult tissues. This activation by guanyl nucleotides may magnify tissue hormonal responses at some stages of development.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000367:Age Factors; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D006321:Heart / Q000187:drug effects*; D009206:Myocardium / Q000201:enzymology*; D051381:Rats
chemical_list: D006165:Guanylyl Imidodiphosphate; D006160:Guanosine Triphosphate; D000262:Adenylyl Cyclases; D004837:Epinephrine