AbstractsBiology & Animal Science

The first mammalian lipoxygenase to be discovered in 1974 was platelet-type 12-lipoxygenase (p12-LO) which was named for the site of its discovery. It belongs to a large family of non-heme dioxygenases including 5-lipoxygenase responsible for leukotriene biosynthesis. Although p12-LO was the first lipoxygenase in mammals to be discovered and research has been going on since the discovery, only very little is known about regulation of activity. Involvement in cancer, angiogenesis, hypertension and platelet activation could be attributed to p12-LO activity and its metabolite 12-HETE and suggests the necessity of intensified research. For this study a focus was put on probable regulation in a sex dependent manner, as androgens had recently been found to be involved in regulation of 5-LO and leukotriene biosynthesis. Additionally, in particular for cardiovascular diseases a gender bias with higher incidence in male has been a long established fact, so a possible sex dependent regulation of p12-LO was proposed. To explore p12-LO regulation in general and to elucidate possible sex dependent regulation in particular, a characterisation of p12-LO regulation in platelets was attempted in this work with two different approaches. One, gender differences in regulation of p12-LO and possible influences of sex hormones were investigated. Two, common pharmacological tools, CDC and MK-886, were used to elucidate possible properties of p12-LO in intact cells. Platelet 12-lipoxygenase is not differently active between the two sexes whether in non-stimulated and stimulated platelets was essentially the same. No differences were manifest in release of AA, subcellular localisation, translocation pattern or protein amount of p12-LO compared in platelets from male and female donors. However, a slight tendency towards lower product formation in female platelets was observed. A strong spontaneous p12-LO activity was measured in non-stimulated platelets and metabolic activity continued over log time periods. p12-LO activity could strongly be enhanced by platelet stimulation with thrombin, collagen, A23187 and arachidonic acid. However, a direct induction of p12-LO activity by these agonists seems improbable. Platelet stimulation rather strongly increases the amount of available substrate for p12-LO as cPLA2 is activated and AA released than activates p12-LO itself. p12-LO activity was potently and selectively suppressed to a basal level by addition of 1 to 3 µM progesterone in a fast and non-genomic manner. Application of the other sex hormones estradiol and DHT failed to show an effect on p12-LO activity. Only p12-LO was affected by progesterone, other enzymes metabolizing AA as cPLA2 and COX-1 were not affected in any circumstances. [Ca2+]i levels, platelet aggregation, subcellular localisation and translocation pattern of p12-LO were not influenced by progesterone. A direct inhibition of p12-LO by progesterone could furthermore be excluded as no progesterone effect could be observed in homogenate incubations. p12-LO activity is not…