GH and IGF-I regulate the expression of endothelial nitric oxide synthase (eNOS) in cardiovascular tissues of...

This study explored whether short-term replacement therapy with growth hormone (GH) affects blood pressure (BP), heart rate (HR) and endothelial nitric oxide synthase (eNOS) expression in cardiovascular tissues in hypophysectomized (Hx) female rats.

BP, HR and the expression of eNOS in the aorta, caval vein and heart were studied in Hx female rats and in Hx female rats that underwent 7 days treatment with GH and thyroxine+glucocorticoids ([T(4)+GC]). Insulin-like growth factor-I (IGF-I) was included in a second experimental protocol to explore the indirect effect of GH. The expression and localisation of eNOS was analysed by immunoblotting and immunohistochemistry.

Decreased BP (Hx 98+/-1, Intact 129+/-3 mmHg, P<0.05), HR (Hx 297+/-14, Intact 399+/-31 beats/min, P<0.05) and unchanged eNOS expression was demonstrated in Hx compared with intact rats. None of the hormones affected BP, but both GH and IGF-I increased HR compared with Hx rats (GH 358+/-10, IGF-I 337+/-7, Hx 306+/-11 beats/min, P<0.05). Replacement of GH, GH+[T(4)+GC] and IGF-I resulted in an increased aortic eNOS expression (GH 161+/-24, GH+[T(4)+GC] 177+/-25, IGF-I 153+/-21, Hx 109+/-7%, P<0.05), whereas in caval vein only GH+[T(4)+GC] affected eNOS expression. None of the hormones changed the level of eNOS in the heart. eNOS was localised in the intima layer of the aorta, whereas in the caval vein eNOS was localised in all cell layers.

These findings support the suggested positive role of GH in the regulation of the cardiovascular homeostasis. The observed up-regulation of eNOS, and presumably an increased NO bioavailability, may result in improved endothelial and cardiovascular function.