Polymorphisms in the IGF1 gene and their effect on growth traits in Mexican beef cattle.

The IGF1 gene (insulin-like growth factor 1) is a candidate gene for marker-assisted selection strategies. A single nucleotide polymorphism in the promoter region (IGF1/SnaBI) has been reported to be associated with production traits in several cattle breeds. Here, we report its allelic frequencies in Charolais and Beefmaster breeds; we confirm its association with three growth traits: weaning weight, weaning weight adjusted to 210 days and preweaning weight gain in the Charolais breed. In addition, we designed a strategy to search these breeds for new polymorphisms in four coding regions of the gene. A C/A transversion was detected in intron 4, but it was not associated with the growth traits. A single nucleotide polymorphism (IGF1/SnaBI) is proposed as a selection marker for Mexican Charolais cattle; validation of its association with weaning weight, weaning weight adjusted to 210 days and preweaning weight gain, could complement the genetic evaluations of this breed through marker-assisted management strategies.

Acute effects of 17beta -estradiol on femoral veins from adult gonadally intact and ovariectomized female pigs.

Our experiments were designed to determine the acute effects of 17beta-estradiol on femoral veins from intact and ovariectomized female pigs. Rings of femoral veins with or without endothelium were suspended in organ chambers for measurement of isometric force. Concentration-response curves to 17beta-estradiol (10(-9) to 10(-5) M) were obtained in veins contracted with prostaglandin F(2alpha) in the absence and presence of inhibitors of either estrogen receptors (ICI-182780; 10(-5) M), nitric oxide synthase [N(G)-monomethyl-l-arginine (l-NMMA); 10(-4) M], soluble guanylate cyclase (1-H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one; 10(-5) M), or potassium channels (tetraethylammonium; 10(-2) M). Estrogen receptors were identified with the use of Western blotting and immunostaining in veins of both groups. 17beta-Estradiol caused acute endothelium-dependent relaxations in both groups. Relaxations to 17beta-estradiol were inhibited by l-NMMA and 1-H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one but not ICI-182780. Tetraethylammonium inhibited relaxations only in veins with endothelium from intact females. Results indicate that 17beta-estradiol causes acute endothelium-dependent relaxations in femoral veins. The relative contribution of nitric oxide and K(+) channels as mechanisms involved in relaxations to 17beta-estradiol in femoral veins is modulated by ovarian status.

Ovariectomy increases mitogens and platelet-induced proliferation of arterial smooth muscle.

Experiments were designed to determine how ovariectomy modulates mitogenic factors in platelets and how these factors affect proliferation of coronary arterial smooth muscle. Platelet-derived growth factors (PDGF(AB) and PDGF(BB)), transforming growth factors (TGF-beta(1) and TGF-beta(2)), and vascular endothelial growth factor (VEGF(165)) were quantified in platelet lysates and platelet-poor plasma from adult gonadally intact and ovariectomized female pigs by ELISA. Proliferation of cultured coronary arterial smooth muscle cells (SMCs) from both groups of pigs was determined in response to autologous or heterologous platelet lysates. Platelet concentrations of PDGF(BB), but not PDGF(AB), TGF-beta(1), and TGF-beta(2), increased with ovariectomy. VEGF(165) was not detected in platelets from either group. Proliferation of SMCs from ovariectomized females was significantly greater on exposure to autologous or heterologous platelet lysates than proliferation of SMCs from intact females. These results indicate that ovariectomy increases concentrations of PDGF(BB) in platelets. Higher levels of PDGF(BB) in platelets in synergy with other platelet-derived products could contribute to increased proliferative arterial response to injury after ovariectomy.

Selected contribution: Effects of sex and ovariectomy on responses to platelets in porcine femoral veins.

Estrogen replacement increases risk of venous thrombosis. In this study, we determined responses in vitro to platelets and platelet products in veins from adult male and intact and ovariectomized female pigs. When contracted with prostaglandin F(2alpha), platelets (25,000 platelets/microl) caused relaxation in veins with endothelium. Higher numbers of platelets caused contraction in veins with and without endothelium. In veins without endothelium, contractions were greater in veins from male than in veins from female pigs, and contractions in intact female pig veins were greater than in ovariectomized females pig veins. Platelet products 5-hydroxytryptamine and thromboxane (analog U-46619) caused comparable contractions in all veins; contractions to prostacyclin were less in veins from intact female pigs. ADP caused comparable endothelium-dependent relaxations in all groups. These relaxations were increased by indomethacin in veins from intact males and females; with inhibition of nitric oxide, relaxations were comparable in all groups. These results suggest that venous responses to platelets vary with sex and presence of ovaries in female pigs. These variations reflect differences in type and quantity of substances released from platelets as well as the sensitivity of the smooth muscle to some vasoactive substances. In addition, products of cyclooxygenase may reduce endothelium-dependent relaxations in veins.

Vascular effects of estrogens: arterial protection versus venous thrombotic risk.

Mechanisms by which estrogen reduces the risk of arterial disease, while simultaneously increasing the risk of venous thrombosis in postmenopausal women, are not clearly understood. In addition to providing beneficial arterial effects on the lipid profile, estrogen both increases production of nitric oxide and decreases production of endothelin-1 from arterial endothelium, decreases intracellular calcium in arterial smooth muscle and might favor fibrinolysis. All of these effects could act in concert to protect against development of arterial occlusive disease. However, comparable effects on venous endothelium and smooth muscle have not been studied systematically, and although blood elements such as platelets and leukocytes contain estrogen receptors, much remains to be learned about the effect that dose and duration of estrogen-treatment might have upon these cells. An integrative approach to understanding the actions of estrogen on the venous system and the interaction of blood elements with the vascular wall is necessary before new therapeutic interventions will provide arterial protection with no risk of venous thrombosis.

Mechanism of relaxations to dendroaspis natriuretic peptide in canine coronary arteries.

Experiments were designed to determine mechanisms by which Dendroaspis natriuretic peptide (DNP) causes relaxations in coronary arteries. Rings of canine left circumflex artery with and without endothelium were suspended in organ chambers filled with Krebs-Ringer bicarbonate solution (37 degrees C, bubbled with 95% O2/5% CO2). Concentration-response curves to DNP (10(-10) to 3 x 10(-7) M) were obtained in arteries contracted with prostaglandin (PGF(2alpha), 2 x 10(-6) M), either in the absence or the presence of C-ANP (10(-6) M) to inhibit natriuretic clearance receptors; indomethacin to inhibit cyclooxygenase (INDO, 10(-5) M), N(G)-monomethyl-L-arginine to inhibit production of nitric oxide (L-NMMA; 10(-4) M), HS-142-1 to inhibit particulate guanylate cyclase (10(-5) M); 1H-[1,2,4]oxadiazolo-[4,3-alpha]quinoxalin-1-one to inhibit soluble guanylate cyclase (ODQ; 10(-5) M), or tetraethylammonium to inhibit potassium channels (TEA; 10(-3) or 10(-2) M). Relaxations to DNP were greater in rings with than in those without endothelium. C-ANP significantly attenuated relaxations to DNP only in rings with endothelium. HS-146-1 but not INDO, L-NMMA, ODQ, and TEA significantly reduced relaxations to DNP in rings with and without endothelium contracted with PGF(2alpha). These results suggest that the endothelium augments inhibitory effects of DNP and that natriuretic clearance receptors mediate this component of the response to DNP in canine coronary arteries. In addition, relaxations to DNP in canine arterial smooth muscle involve activation of particulate guanylate cyclase but not hyperpolarization.

Activation of soluble guanylate cyclase and potassium channels contribute to relaxations to nitric oxide in smooth muscle derived from canine femoral veins.

Experiments were designed to examine mechanisms of relaxations to nitric oxide (NO) in venous smooth muscle. Rings of canine femoral veins without endothelium were suspended for measurement of isometric force in organ chambers. Concentration-response curves to NO and 8-Br-cyclic guanosine monophosphate (cGMP) were obtained in veins contracted with KCl (60 mM) or prostaglandin F2alpha (PGF2alpha; 2x10(-6) M) in the absence and presence of inhibitors of soluble or particulate guanylate cyclase or K+ channel antagonists. In rings contracted with PGF2alpha, relaxations to NO were reduced significantly by inhibition of soluble but not particulate guanylate cyclase. Relaxations to NO were reduced in rings contracted with KCI. Tetraethylammonium (10(-2) M) and glibenclamide (10(-7) M) + charybdotoxin (10(-7) M) significantly reduced relaxations to NO in rings contracted with PGF2alpha. Relaxations to 8-Br-cGMP were decreased significantly only by charybdotoxin. These results suggest that relaxations to NO in canine femoral veins involve at least two intracellular processes: activation of soluble guanylate cyclase and activation of adenosine triphosphate (ATP)-sensitive and large-conductance, Ca+2-activated K+ channels. The large-conductance, Ca+2-activated K+ channels seem to be activated by cGMP-dependent mechanisms. Therefore relaxations to NO in venous smooth muscle involve intracellular processes similar to those in arterial smooth muscle.