GH1 and acromegaly: In fact, a recent study has shown that GH levels directly correlated to the severity of ED in 51 males with acromegaly and that Nitric Oxide (NO) levels were significantly lower in acromegalic patients than in non-acromegalic controls [14], supporting the hypothesis of acromegaly as a direct cause of endothelial dysfunction, as previously suggested by other authors [18].