Meptazinol and Pentazocine: Effects on Prolactin, Growth Hormone and Vasopressin Levels in Plasma

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Abstract
The effects of two partial agonist opioid analgesics, meptazinol (at doses 0.7 and 1.4 mg/kg intravenously) and pentazocine (at doses 0.3 and 0.6 mg/kg), on anterior and posterior pituitary hormone secretion were studied in six normal human volunteers. Both drugs stimulated the secretion of prolactin dose‐dependently, as expected. This effect was seen in all subjects, although two of the six subjects reacted more sensitively to both drugs. Plasma growth hormone concentrations were increased only after the higher dose of meptazinol. This was also seen in all subjects suggesting a spesific pharmacological effect. Vasopression (AVP) in plasma was greatly increased (up to 76 pg/ml) in three of the six subjects after the higher dose of meptazinol, but remained on a low level in the other three and after all other drug doses. The increase in AVP occurred only in those individuals who reported nausea after meptazinol. It was concluded that the augmented AVP release following meptazinol administration was likely to be a non‐specific response induced by nausea and not an effect mediated by opiate receptors.