The influence of sex and different segments of thoracic aorta on bioactive aortic substance (BAS) and prostacyclin (PGI2) synthesis

Arachidonic acid metabolism by adult human osteoblast-like cells exhibits sexually dimorphic characteristics

The eicosanoids, including prostaglandin E2 (PGE2) and other bioactive arachidonic acid metabolites, are important local mediators of bone remodeling. Presumably, the limited or excessive synthesis of the eicosanoids could compromise bone homeostasis. We have noted that the stimulated release of arachidonic acid by adult male donor derived human osteoblast-like (hOB) cells exceeded the stimulated release measured for female-derived hOB cells by 1.5-fold. Assays of PGE2 biosynthesis by cytokine-stimulated hOB cells also demonstrated a sex-linked difference, such that male hOB cell PGE2 production exceeded female cell production by 1.6-2.2-fold. The calcium-dependent cytoplasmic phospholipase A2 activity in subcellular fractions prepared from hOB cell homogenates was higher in both the cytosolic (1.6-fold) and particulate (1.5-fold) fractions from the male cells than in those prepared from female hOB cells, suggesting a molecular basis for the observed sexually dimorphic characteristics related to arachidonic acid metabolism by hOB cells. The relatively limited capacity of the female cells may limit needed intracellular and intercellular signaling during bone remodeling, thereby contributing to the development of bone pathology.

Estrogen increases male rat aortic endothelial cell (RAEC) PGI2 release

Estrogen has been proposed as a negative risk factor for development of peripheral vascular disease yet mechanisms of this protection are not known. This study examines the hypothesis that estrogen stimulates rat aortic endothelial cell (RAEC) release of PGI2. Male Sprague-Dawley rat abdominal aortic 1-mm rings were placed on 35 mm matrigel plates, and incubated for 1 week. The cells were transferred to a Primaria 60-mm dish and maintained from passage 3 in RAEC complete media and experiments performed between passages 4-10. Cells were incubated with Krebs-Henseleit buffer (pH 7.4) containing carrier or increasing concentrations of beta-estradiol or testosterone for 60 min. The effluent was analyzed for eicosanoid release of 6-keto-PGF1 alpha (6-keto, PGI2 metabolite), PGE2 and thromboxane B2 (TXB2) by EIA (hormone stimulated-basal). Cells were analyzed for total protein by the Bradford method and for cyclooxygenase-1 (COX-1) and prostacyclin synthase (PS) content by Western blot analysis and densitometry. Testosterone did not alter RAEC 6-keto-PGF1 alpha release, whereas estrogen increased RAEC 6-keto-PGF1 alpha release in a dose-related manner. Estrogen preincubation (10 ng/ml) decreased COX-1 and PS content by 40% suggesting that the estrogen-induced increase in male RAEC PGI2 release was not due to increased synthesis of COX-1 or PS. These data support the hypothesis that estrogen stimulation can increase endogenous male RAEC release of PGI2.

Regional differences in prostaglandin production rates among porcine intrathoracic vessels

To investigate the regional variability in intrathoracic vascular prostaglandin (PG) synthesis, we obtained vessel segments from porcine coronary artery (COA), thoracic aorta (AT), common carotid artery (CRA), pulmonary artery (PA), pulmonary vein (PV), and inferior vena cava (IVC). Vascular production rates of 6-keto-PGF1 alpha (an indicator for PGI2), PGF2 alpha, and PGE2 were measured both in unstimulated state and in arachidonic acid-stimulated state using immunosorbent assays. Our results indicated that PGI2 production rate in all vessel segments decayed with time after vessel dissection. In all vessel segments tested under unstimulated conditions, PGI2 production rates were about one order of magnitude higher than PGF2 alpha and PGE2 production rates of the same specimens. Results from unstimulated, 1.5 hr pre-incubated specimens indicated that i) PGI2 production rates in COA, AT, and PV were greater than those in CRA, PA, and IVC; ii) PGF2 alpha production rates from the same specimens were higher in PV than in AT, CRA, and IVC, while these in PA were higher than in IVC; and iii) PGE2 production rates from the same specimens were not significantly different from one another. Arachidonic acid added at about 1.5 hr after vessel harvest stimulated the PGI2 and PGF2 alpha synthesis rates by 3 to 15 folds. However, this arachidonic acid treatment caused 70 to 300-fold increases in PGE2 production rates, reaching levels comparable to PGI2. All three prostanoid production rates under stimulated conditions were also variable among different intrathoracic vessels. Although either physiological gas concentrations or local hemodynamic conditions alone can partially explain our results, which physiological parameter(s) actually causes these regional differences remains to be verified.