Direct effect of adenosine on prolactin secretion at the level of the single rat lactotroph: involvement of pertussis toxin-sensitive and -insensitive transducing mechanisms.
We studied the effect of adenosine on prolactin secretion by the anterior pituitary, and the transduction mechanisms whereby the purine exerts its action. Adenosine inhibited prolactin release in basal and in vasoactive intestinal peptide (VIP)- or TRH-stimulated conditions. Pertussis toxin pretreatment reduced the inhibition of VIP-stimulated prolactin secretion which was induced by adenosine, while it completely abolished the effect of the purine on TRH-evoked prolactin release. In membrane preparations of anterior pituitary cells, adenosine reduced the adenylate cyclase activity stimulated by VIP. Such an inhibition was not blocked by pertussis toxin pretreatment. Furthermore, the purine reduced TRH-stimulated inositol phosphate production in cultured anterior pituitary cells, an effect that was reversed by pretreatment with pertussis toxin. In addition, the nucleoside did not significantly affect the TRH-induced rise in intracellular calcium. In conclusion, our data show that adenosine inhibits prolactin secretion, acting on purinergic receptors coupled to the adenylate cyclase enzyme and phospholipase C. The effect of the nucleoside on adenylate cyclase seems to be achieved either by the involvement of an adenosine receptor coupled to the catalytic subunit of the enzyme via a pertussis toxin-sensitive G protein, or by the activation of a site directly coupled to the catalytic subunit of the adenylate cyclase (the P site). Its effect on phospholipase C seems to be mediated by a purinergic receptor coupled to the intracellular effector via a pertussis toxin-sensitive G protein.
Scorziello
A
A
Dipartimento di Scienza delle Comunicazioni Umane, Facoltà di Medicina e Chirurgia, Università di Napoli Federico II, Italy.
Landolfi
E
E
Grimaldi
M
M
Meucci
O
O
Ventra
C
C
Avallone
A
A
Postiglione
A
A
Schettini
G
G
D000241:Adenosine / Q000494:pharmacology*; D037361:Adenylate Cyclase Toxin; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000096:biosynthesis; D037342:Pertussis Toxin; D010903:Pituitary Gland, Anterior / Q000187:drug effects* / Q000378:metabolism*; D011388:Prolactin / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D018047:Receptors, Purinergic P1 / Q000187:drug effects / Q000502:physiology; D015290:Second Messenger Systems / Q000187:drug effects / Q000502:physiology; D013973:Thyrotropin-Releasing Hormone / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism; D014660:Vasoactive Intestinal Peptide / Q000494:pharmacology; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
D037361:Adenylate Cyclase Toxin; D007295:Inositol Phosphates; D018047:Receptors, Purinergic P1; D010566:Virulence Factors, Bordetella; D014660:Vasoactive Intestinal Peptide; D013973:Thyrotropin-Releasing Hormone; D011388:Prolactin; D037342:Pertussis Toxin; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D000241:Adenosine; D002118:Calcium