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85 CARDIOVASCULAR RESPONSES TO ALPHA MSH IN THE FETAL AND NEWBORN SHEEP

The cardiovascular effects of alphaMSH and related peptides have not been studied extensively. Although there are some observations of adult animals, no studies have been conducted of the fetal and neonatal circulation. Therefore we examined the responses to an i.v. bolus of 75 micrograms of alphaMSH on heart rate (HR) mean arterial pressure (MAP), aortic blood flow (ABF), and stroke volume (SV) in 9 newborn lambs (15 to 27 days) and in fetal sheep (110 to 133 days gestation). An increase in ABF and decrease in MAP was observed following alphaMSH injection in the fetus (140 ± 38 to 158 ± 40 ml/Kg/min, p 0.005 and 41.7 ± 1.8 to 39.0 ± 1.6 mm Hg p 0.0125 respectively) (mean ± SE). There was no significant modification of fetal HR or SV. In the newborn, there was an increase in ABF (257 ± 25 to 326 ± 33 ml/Kg/min, p 0.005) and HR (106 ± 8 to 122 ± 10 beats/min, p 0.005) and a decrease in MAP (73 ± 4 to 69 ± 5, p 0.005) after alphaMSH injection. There was no modification of the SV in the newborn lamb. Beta blockade with propranolol (lmg/Kg) did not prevent the rise in ABF and HR observed after the same dose of alphaMSH in the newborn lamb. These results indicate that alphaMSH is able to increase the left ventricular output in the newborn and fetal sheep and its mechanism of action is not through beta adrenergic receptor (Supported by NIH Grant HLO6285 and HD06619).