Interactive effects of growth hormone and oestrogen on vascular responses in hypophysectomised female rats

Growth hormone (GH) and oestrogen (E(2)) are associated with beneficial effects on the cardiovascular system and it is therefore of great interest to study their interactive effects on haemodynamics and vascular function.

Female hypophysectomised (Hx) rats were treated for seven days with GH, E(2) or a combination of the hormones. Systolic blood pressure (SBP), heart rate (HR) and plasma insulin-like growth factor-I (IGF-I) were measured. Contractile properties and endothelial function were studied in isolated resistance arteries using the wire-myograph technique.

Hypophysectomy, per se, caused a fall in SBP and HR, while vascular adrenergic reactivity (sensitivity to applied noradrenaline) was enhanced. Impaired acetylcholine-induced relaxation and basal release of nitric oxide, suggests endothelial dysfunction after Hx. After supplementation with GH, SBP remained low while HR increased towards the control level. GH increased plasma IGF-I, but had no effect on vascular contractility or endothelial responses. E(2) replacement resulted in blunted plasma IGF-I, while the vascular adrenergic and serotonergic responses were reinforced. Endothelial function was not improved after E(2) treatment. When GH and E(2) were given in combination, the GH-induced increase in body weight, plasma IGF-I levels and HR were counteracted by E(2). Moreover, the anticipated reinforcement of the vascular serotonergic response by E(2) was reduced. Neither E(2) nor GH+E(2) affected SBP.

The results suggest that GH and E(2) might have interactive effects on haemodynamic and metabolic parameters, but not on the contractility or endothelial function of resistance arteries, in Hx female rats.