ATRIAL-NATRIURETIC-PEPTIDE (ANP) AS A STIMULUS OF THE HUMAN ACROSOME REACTION AND A COMPONENT OF OVARIAN FOLLICULAR-FLUID - CORRELATION OF FOLLICULAR ANP CONTENT WITH IN-VITRO FERTILIZATION OUTCOME

Atrial natriuretic peptides (ANPs) from several species induced the hu man acrosome reaction. The maximal response was highest for human ANP (18.6% above unstimulated or baseline values) and decreased progressiv ely for peptides derived from animals lower on the phylogenetic scale. ANP concentrations required for a half-maximal effect in noncapacitat ed spermatozoa ranged from 0.07 to 0.38 nM. ANP induced the acrosome r eaction in capacitated spermatozoa, but the concentration required was higher than in noncapacitated cells. The response in noncapacitated s permatozoa was independent of added extracellular Ca2+ and was complet ely inhibited by 1 mu M LY83583 (inhibits particulate guanylate cyclas e). However, 10 mu M N omega-nitro-L-arginine (inhibits soluble guanyl ate cyclase) had no effect. ANP (80 pM) and 3 mu M 1,2-dihexanoyl-sn-g lycerol each induced a nearly half-maximal acrosome reaction. Added in combination, they produced no increased response, suggesting antagoni sm. Follicular fluid had variable levels of immunoreactive ANP. Averag e ANP content was nearly zero in samples that contained no oocyte at t he time of aspiration but was higher (6.9 pM; 90% confidence limits = 1.67-28.72 pM) in follicular fluid containing oocytes that did not fer tilize in vitro. Highest concentrations of ANP were present in follicu lar fluid containing oocytes that fertilized in vitro (72.8 pM; 90% co nfidence limits = 38.1-139.1 pM). These data suggest that noncapacitat ed spermatozoa can acrosome react without added extracellular Ca2+ in response to an extracellular ligand. Also, human spermatozoa appear to contain receptors for ANP similar to those found in other cell types. The ANP content of follicular fluid might partly explain the ability of follicular fluid to induce the acrosome reaction.