Effect of exercise training on cardiac oxytocin and natriuretic peptide systems in ovariectomized rats

Abstract

Exercise training results in cardiovascular and metabolic adaptations that may be beneficial in menopausal women by reducing blood pressure, insulin resistance, and cholesterol level. The adaptation of the cardiac hormonal systems oxytocin (OT), natriuretic peptides (NPs), and nitric oxide synthase (NOS) in response to exercise training was investigated in intact and ovariectomized (OVX) rats. Ovariectomy significantly augmented body weight (BW), left ventricle (LV) mass, and intra-abdominal fat pad weight and decreased the expression of oxytocin receptor (OTR), atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), and guanylyl cyclase-A (GC-A), in the right atrium (RA) and LV, indicating estrogenic control of these genes. These effects of ovariectomy were counteracted by 8-wk-long exercise training which decreased fat pad weight (33.4 +/- 2.3 to 23.4 +/- 3.1 g, n = 8, P < 0.05), plasma free fatty acids (0.124 +/- 0.033 to 0.057 +/- 0.010 mM, n = 8, P < 0.01), and plasma triacylglycerol (0.978 +/- 0.174 to 0.588 +/- 0.115 mM, n = 8, P < 0.05). Chronic exercise tended to decrease BW and stimulated ANP (4- to 5-fold) and OTR gene expression in the LV and RA and BNP and inducible NOS (iNOS) mRNA in the LV. In sham-operated rats, exercise augmented ANP expression in the RA, downregulated GC-A mRNA in the LV and RA, but increased its expression threefold in the RA of OVX animals. Endothelial NOS and iNOS expression was enhanced in the left atrium of sham-operated rats. Altogether, these data indicate that in OVX animals, chronic exercise significantly enhances cardiac OT, NPs, and NOS, thus implicating all three hormonal systems in the beneficial effects of exercise training.

Effects of Aerobic Training on the Cardiomyocytes of the Right Atrium of Mice

“…First, mice subjected to aerobic training exhibited a significant increase in the number and sizes of NP granules from cardiomyocytes compared to sedentary animals, indicating that aerobic training activated the biosynthetic process in cardiomyocytes 3 . These data confirm previously results obtained by Barletta et al 5 , Ohba et al 6 , Edwards 7 and Gutkowska et al 14 . Second, the density of nuclear pores and the relative volumes for euchromatin, mitochondria, endoplasmic reticulum and of Golgi complex were significantly elevated in mice after eight-wk aerobic training.…”

“…The natriuretic and diuretic actions of NPR-A result from enhanced glomerular filtration and/or decreased tubular reabsorption of sodium and water, suppression of renin, aldosterone, and vasopressin secretion as well as antagonism of most of the peripheral and central effects of angiotensin II 19,21 . If the chronic training promotes a parallel increase of NPRs and NPs, then this also explains the concomitant increased production of NO and NPs 22 , observed by Gutkowska et al 14 .…”

Cardiac oxytocin receptor blockade stimulates adverse cardiac remodeling in ovariectomized spontaneously hypertensive rats

“…This study documented that in Sprague-Dawley (SD) rats, ovariectomy reduced OTRs in the left ventricle (LV), as well as also reducing the influence of physical forces on OTRs, ANP, and NO synthase expression (17). We also showed increased OTRs and endothelial NO synthase (eNOS) in the aortic tunica intima of OVX rats treated for 10 days with 17␤-estradiol or genistein, the phytoestrogen (42).…”

“…Western blot analysis was conducted as described elsewhere (17). Blots were incubated overnight at 4°C with mouse monoclonal antibodies for ER-␣ and rabbit polyclonal antibodies for ER-␤ (BD Biosciences, San Jose, CA).…”

“…The increased OTRs in the atria and ventricles of ovariectomized (OVX) rats was reported as an effect of endurance training accompanied by the reduction of cardiac hypertrophy and by beneficial outcomes on body composition (17). This study documented that in Sprague-Dawley (SD) rats, ovariectomy reduced OTRs in the left ventricle (LV), as well as also reducing the influence of physical forces on OTRs, ANP, and NO synthase expression (17).…”