Inhibitory effect of 5‐hydroxytryptamine on penile erectile function in the rat

1 An increase in corporal pressure was elicited in pithed rats by stimulation of the sacral part of the spinal cord. This response was inhibited by intravenous injection of 5‐hydroxytryptamine (5‐HT) (ED50 = 28.5 ± 2.2 μg kg−1). 2 The inhibitory effect of 5‐HT was blocked by methysergide and methiothepin (each 1 mg kg−1), but not by ketanserin (0.02 mg kg−1), MDL 72222 (1 mg kg−1) or prazosin (0.1 mg kg−1). 3 An inhibitory effect on the corporal pressure response to spinal stimulation was also produced by 5‐carboxyamidotryptamine (ED50 = 5.6 ± 2.8 μg kg−1), but not by m‐chlorophenylpiperazine (mCPP), RU 24969, 8‐hydroxy‐2‐[di‐n‐propyl‐amino]‐tetralin (8‐OH‐DPAT) or fenfluramine (doses up to 1–2 mg kg−1). 4 Neither methiothepin (1 mg kg−1) nor clomipramine (1 mg kg−1) had any effect on the frequency‐response curve for increase in corporal pressure by spinal stimulation. 5 The results indicate that 5‐HT exerts an inhibitory action on penile erection by a peripheral mechanism. This effect may be mediated by vasoconstriction in cavernosal vessels, or inhibition of release of a vasodilator neurotransmitter. From the spectrum of agonist and antagonist responses, the receptor involved may be of the 5‐HT1D subtype.