ESTROGENS MODULATE CONTRACTILE EFFECT OF SEROTONIN IN AORTA FROM FEMALE MIDDLE AGED SENESCENCE-ACCELERATED MICE

S. Novella1,2, P. Medina2, A. P. Dantàs3, C. Bueno-Betí1, G. Segarra2, C. Hermenegildo1,2. 1Hospital Clínico Valencia, Research Foundation INCLIVA, Spain, 2University of Valencia, Department of Physiology, Spain, 3Hospital Clínic Barcelona, IDIBAPS, Spain

Aim. Serotonin is an important neurohormonal factor that has been implicated in the regulation of vascular tone. In the cardiovascular system, estrogens regulate expression of several serotonin signalling components. Therefore, the present study was designed to investigate the effects of the ovariectomy on vascular reactivity to serotonin of aortas from senescence-accelerated mice (SAMP8) and senescence-resistant mice (SAMR1), as experimental model to study vascular changes during aging and menopause.

Methods. Five-month-old female SAMP8 (n = 21, weight range: 25.2 to 26.6 g) or SAMR1 (n = 21, weight range: 22.7 to 24.5) were used. Mice were divided into three groups: sham-operated, ovariectomized and ovariectomized plus estradiol. Twenty eight days after surgery, mice were anesthetized and blood samples were withdrawn by cardiac puncture and plasma levels of glucose, creatinine, and 17β-estradiol were determined. Thoracic aortas were collected. Vascular rings (4 mm long) were mounted for isometric recording of tension in organ baths at 37 ºC containing Krebs-Henseleit solution and cumulative concentration-response curves for serotonin (10-8 - 10-5 M) were performed. A segment of thoracic aorta from mice of each group was immediately frozen for protein expression studies. Differences between were analysed by ANOVA, followed by Bonferroni’s post-test to compare replicate means. Statistical significance was accepted at P < 0.05.

Results. Body weight of SAMP8 mice was significantly lower than that of SAMR1. Changes in estrogens plasma levels by ovariectomy and estrogen treatment were similar in both strains. As expected, estrogens decreased with ovariectomy (P<0.05), assuring the efficacy of the surgical process. Estrogen treatment prevented the loss in estrogens by ovariectomy to similar levels as seen in Sham females. These data demonstrate the effectiveness of estrogen dose used to treat ovariectomized mice. Plasmatic concentration of glucose and creatinine were not affected by ovariectomy or estrogen treatment in both SAMR1 and SAMP8 groups. In sham operated-group maximal contraction to serotonin of SAMP8 aortas was similar than in SAMR1 (846±39 vs 855±42, respectively) suggesting that senescence did not affect contractile response to serotonin in female mice. In SAMR1, ovariectomy or ovariectomy plus estrogen treatment did not change (P>0.05) the contractions to serotonin. Maximal contractile responses to serotonin of aortic rings from SAMP8 were enhanced by ovariectomy (855±42 vs 1071±51, P<0.05, respectively), and estradiol supplementation prevented the effects of ovariectomy. Molecular studies on protein expression supported the results obtained in organ baths.

Conclusions. These data reveal that at age of six months (middle age) SAMP8 mice did not change the contraction to serotonin, probably because these mice have a good ovarian function and normal plasma levels of estrogens. Ovariectomy and reduction of estrogen plasma levels increase the contractions to serotonin in SAMP8 mice, an effect that is completely prevented by exogenous administration of estradiol.