Mechanisms of action of angiotensin II on mammalian sperm function

Abstract

Angiotensin II (AII) stimulates capacitation and fertilizing ability in mammalian spermatozoa, with the binding of AII to its receptors resulting in stimulation of cAMP production in both uncapacitated and capacitated cells. This study investigated possible mechanisms whereby AII affects cAMP availability. The first question was whether extracellular Ca 21 is required for responses in mouse spermatozoa and, using chlortetracycline fluorescence analysis, it was clear that cells responded to AII only when the medium contained CaCl 2 , with both 90 mM and 1.80 mM supporting a significant acceleration of capacitation. Consistent with those results, AII significantly stimulated cAMP production in both CaCl 2 -containing media tested, the response being greater in that containing 1.80 mM. Several different agents that might affect the signalling pathway stimulated by AII were then evaluated in uncapacitated suspensions. Chlortetracycline analysis revealed that pertussis toxin abolished responses to AII, suggesting the involvement of an inhibitory Ga subunit; dideoxyadenosine, a specific membrane-associated adenylyl cyclase (mAC) P-site inhibitor, also blocked responses, suggesting involvement of an mAC. cAMP determinations confirmed that both reagents also abolished AII's stimulation of cAMP. In contrast, nifedipine, a Ca 21 channel blocker, did not inhibit AII's effects on spermatozoa. Finally, in capacitated suspensions, both pertussis toxin and dideoxyadenosine were again shown to block AII's stimulation of cAMP. These results suggest that responses to AII involve an inhibitory G protein and an mAC, but it is likely that AII -receptor coupling does not stimulate directly mAC but rather does so in an indirect manner, perhaps by altering the intracellular Ca 21 concentration.Reproduction (2005) 129 211-218

Effects of estrogenic xenobiotics on human and mouse spermatozoa

“…Consistent with other studies we have carried out (e.g. Mededovic and Fraser, 2005), pertussis toxin on its own had no detectable effect (Figure 9). However, when used in combination with genistein and daidzein, it was able to block the usual stimulatory responses obtained with these xenobiotics.…”

“…Uncapacitated mouse sperm suspensions were incubated for approximately 35 min in the presence of 10 nmol/l genistein with/without 100 μmol/l ddAdo (n = 3). Used on its own, ddAdo had no significant effect, again consistent with other studies using ddAdo in a similar system (Baxendale and Fraser, 2003a;Mededovic and Fraser, 2005). When used with genistein, however, ddAdo essentially blocked the responses to the xenobiotic ( Figure 10).…”

“…One possibility is that the inhibitory G proteins are inhibiting a Ca 2+ extrusion mechanism such as Ca 2+ -ATPase or a Na + /Ca 2+ exchanger. A similar mechanism involving inhibitory proteins has been suggested for angiotensin II and its G-protein-coupled receptor (Mededovic and Fraser, 2005).…”

Regulation of mammalian sperm capacitation by endogenous molecules

“…Further investigation confirmed that pertussis toxin does indeed have different effects on responses to FPP and to AII, suggesting that the initial step in response to these two first messengers is different for the two peptides. Since both stimulate cAMP production in uncapacitated suspensions, it seems likely that binding of AII to its receptor stimulates cAMP in an indirect manner, possibly by altering intracellular Ca 2+ concentration (18). Immunolocalization studies revealed that AII receptors ,like the receptors for FPP, adenosine and calcitonin, are located on both the acrosomal cap and along the flagellum of mouse and human spermatozoa (17).…”

A cascavel Crotalus durissus terrificus (Viperidae: Crotalinae) como modelo experimental para o estudo do envolvimento de peptidases na sobrevida de espermatozóides

“…Os peptídeos são degradados por um limitado número de enzimas com uma especificidade de substrato relativamente ampla (ROQUES et al, 1993) (VINSON et al, 1995;KÖHN et al, 1998). A AngII aumenta a motilidade, hiperativa e capacita o espermatozóide (VINSON et al 1996), porém não inibe a perda espontânea do acrossoma, tanto em espermatozóides humanos quanto de ratos (MEDEDOVIC & FRASER, 2005). A AngII eleva a concentração de AMPc em espermatozóides capacitados e incapacitados (MEDEDOVIC & FRASER, 2004).…”