1. The changes in blood pressure in response to parenteral administration of
bombesin, the active tetradecapeptide of the skin of the European discoglossid frogs Bombina bombina and Bombina variegata variegata have been investigated in some experimental animals.2. In most species, the
polypeptide elicited
hypertension which was usually gradual in onset and slow to disappear. Blood pressure increases rarely exceeded 40-50 mmHg. At the beginning of an experiment some dose-response relationship could often be observed, but later tachyphylaxis developed. During an
intravenous infusion of
bombesin the rise in blood pressure could sometimes be maintained at a steady level as long as the infusion was continued, but at other times, the rise of pressure slowly subsided with continued administration of the
polypeptide. In the rat and the chicken
hypertension elicited by high doses of
bombesin was often followed by secondary
hypotension.3.
Bombesin-induced
hypertension was apparently not affected by pretreatment with either alpha- or
beta-adrenergic blocking agents. Similarly secondary
hypotension was not abolished by
atropine. Thus, the effect of
bombesin on vascular smooth muscle seems to be predominantly a direct one.4.
Angiotensin was usually more potent than
bombesin, and its effect on blood pressure was more rapid and of shorter duration. Tachyphylaxis to
angiotensin was lacking or moderate.5. In sharp contrast to the other species, the monkey responded to
bombesin with frank
hypotension, which was usually proportional to the dose. In the monkey the hypotensive effect of
bombesin was equal to, or greater than that of
eledoisin or
physalaemin and
bombesin-
induced hypotension was of longer duration than that of the other
polypeptides. Tachyphylaxis was moderate for low and adequately spaced doses of the
polypeptide, but prompt and intense for high doses. Long-lasting
hypotension was obtained by
intravenous infusion of
bombesin, but repeated infusions caused tachyphylaxis.
Bombesin-
induced hypotension was not affected by pretreatment with
atropine.6.
Bombesin may be easily distinguished from all other known
peptides active on vascular and extravascular smooth muscle by its effects on blood pressure. This does not apply to
bombesin-like
peptides, such as
alytesin and
ranatensin.