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We investigated, using guinea-pig spermatozoa as a model, whether phospholipase A2 (PLA2) is involved in progesterone or zona pellucida (ZP)-stimulated acrosomal exocytosis, if progesterone enhances ZP-induced activation of PLA2, and mechanisms underlying PLA2 regulation. Spermatozoa were capacitated and labeled in low Ca2+ medium with [14C]choline chloride or [14C]arachidonic acid, washed, and then exposed to millimolar Ca2+ and progesterone and/or ZP. Each agonist stimulated decrease of phosphatidylcholine (PC) and release of arachidonic acid and lysoPC, indicative of PLA2 activation. Aristolochic acid (a PLA2 inhibitor) abrogated lipid changes and exocytosis, indicating that these lipid changes are essential for exocytosis. Exposure of spermatozoa to submaximal concentrations of both progesterone and ZP resulted in a synergistic increase of arachidonic acid and lysoPC releases, and exocytosis, suggesting that, under natural conditions, both agonists interact to bring about acrosomal exocytosis. Progesterone-induced PLA2 activation appears to be mediated by a GABA(A)-like receptor, because bicuculline (a GABA(A) receptor antagonist) blocked arachidonic acid release and exocytosis. In agreement with this, GABA mimicked progesterone actions. ZP-induced activation of PLA2 seemed to be transduced via G(i) proteins because pertussis toxin blocked arachidonic acid release and acrosomal exocytosis. PLA2 may be regulated by PKC because progesterone- or ZP-induced release of arachidonic acid was blocked by the PKC inhibitors staurosporine or chelerythrine chloride. PLA2 could also be regulated by the cAMP-PKA pathway; inclusion of the PKA inhibitor 14-22 amide or H-89 led to a reduction in arachidonic acid release or exocytosis after progesterone or ZP. Taken together, these results suggest that PLA2 plays an essential role in progesterone or ZP-stimulated exocytosis with progesterone priming ZP action.

Myocardial infarction (MI)-prone Watanabe hereditary hyperlipidemic (WHHLMI) rabbits were reported to spontaneously but slowly develop MI, associated with enhanced coronary atherosclerosis and metabolic syndrome features. Our aim was to accelerate these processes by exposing the rabbits to a high-fat diet (HFD) that was previously shown to induce insulin resistance and cardiac injury in rabbits. HFD feeding for one year was indeed associated with development of obesity (37% increases in body weight, as compared to 3.7% for control standard-fat diet, SFD). On HFD, liver weight and hepatic triglyceride content were significantly higher as compared to SFD, with mild steatosis. Glucose and insulin levels were not markedly different on SFD or HFD, however after 1 year of diet treatment, HFD-fed animals were more glucose intolerant as compared to SFD-fed rabbits. On SFD, the rabbits developed marked thoracic aorta stenosis and calcification of atherosclerotic lesions, which were not aggravated by HFD feeding. Cardiac function analysis by MRI and transthoracic echocardiography did not reveal significant differences between SFD-and HFD-fed rabbits. Thus, the metabolic and cardiac phenotype of WHHLMI rabbits was not aggravated by HFD feeding for one year, and the rabbits did not spontaneously develop diabetes or myocardial infarction.

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