THE INFLUENCE OF PARATHYROID AND SEX HORMONES ON THE PACEMAKER AND CONTRACTILE ACTIVITY OF THE FROG ISOLATED HEART

The impairment of the hormonal regulation of the calcium systemic and cellular metabolism is one of the forcible causes of the cardiovascular system disorders. Calcium homeostasis maintenance depends on the status of the calcium-regulating system (parathyroid hormone -thyrocalcitonin - vitamin D-3), but, anyway, the participation of the sex hormones in its regulation is not excluded. The aim of the present investigation is to reveal the effects of parathyroid and sex hormones on the pacemaker and contractile activity of the heart. By the method of opto-electronic regulation of the heart contractions in the dynamic regimen a comparative analysis of the influence of the parathyroid hormone 1-34 active fragment (1-34 PTH) of both female (beta-estradiol) and male (testosterone) sex hormones on the contraction frequency and amplitude of the frog's isolated heart was conducted. The independent effects of the mentioned hormones, as well as their combined influence (1-34-PTH/estradiol and 1-34-PTH/testosterone) on the dynamics of the frequency and amplitude feature changes of the heart contraction were investigated. The monitoring of the obtained results points at the positive chronotropic and inotropic-stabilizing effects of 1-34-PTH. It was revealed that the sex hormones possess positive cardiotropic effect as well, but it is more expressed in beta-estradiol action. In spite of the positive cardiotropic effect of testosterone, the latter, nevertheless, sharply contracts the viability of the frog's isolated heart as it stopped already at the 20th minute of the experiment whereas 1-34-PTH and estradiol supported the heart functioning for more than 50-60 minutes. The combined influence of 1-34-PTH with estradiol reveals the modulating effect of PTH which somehow smoothes out the positive chronotropic-inotropic shifts observed in beta-estradiol's action. In this way it prevented excessive activation of the heart contractions ("phenomenon of enraged heart pacification"). In case of the combination with testosterone the mentioned fragment of parathyroid hormone displays cardio-protecting activity which was expressed when supporting the viability of the isolated heart. Thus, 1-34-PTH corrects sharp changes of the functional indices of the heart observed under the influence of sex hormones and makes their shifts practically identical both in time and direction.