The influence of ketanserin, a new S2 receptor antagonist on experimentally induced skeletal muscle myopathy in the rat

Effects of a serotonin S2-receptor blocker on healing of acute and chronic tendon injuries

The beneficial effects of serotonin S(2)-receptor blockers on healing skin and muscle ulcers and refractory lesions such as leprosy and diabetic and ischemic ulcers have been reported previously, but their mechanisms of actions are not clear. The present study sought to elucidate the action of an S(2)-receptor blocker, metrenperone, on the healing of collagenase-induced injuries in superficial digital flexor tendons of two groups of rabbits. In one group, oral and topical therapy for 28 days with metrenperone, was started within 48 hr of a single acute injury. The animals were then left untreated for another 60 days, when it was found that most of the morphological, biochemical, and biomechanical characteristics of the healed tendons matched those of their normal uninjured controls. Injured, untreated controls showed poor healing. In the second group of animals, tendon injury was induced by four separate injections of collagenase at weekly intervals. The rabbits were left for another 60 days, before being treated with metrenperone for 26 days. This delayed treatment had no apparent effect on the biomechanical, biochemical, or morphological characteristics of the healing tendons. It appeared that metrenperone had a significant effect on collagen turnover and organization of scar tissue, but only while the inflammatory and fibroplastic processes were active in the early stages of healing. S(2)-receptor blockers may, therefore, be of potential value for modulating repair in acutely injured collagenous tissue.

Oversensitivity to serotonin of the collateralized vascular bed in rat hindquarters: mechanisms of increased vasoconstriction

A buffered solution was perfused at a constant flow rate (2 ml/min) through both iliac arteries in rat hindquarters. Perfusion pressures were measured in normal and collateralized vascular beds of the left and right hind-leg, respectively. Bolus injections of various agonists produced concentration-dependent increases in perfusion pressure in both collateralized and normal circulatory beds. Serotonin, in particular, and noradrenaline, to a lesser extent, produced more pronounced vasoconstriction on the collateral side than on the normal side. The difference in vasoreactivity to serotonin was related to a difference in both vascular structure and sensitivity of both types of vascular bed. Vasoconstriction induced by serotonin was inhibited by 5-HT2 antagonists. Selective blockade of alpha 1,alpha 2,beta 1-beta 2 adrenoceptors and amine uptake blockade were ineffective. This study indicates that, in rat hind-legs, the collateralized vascular bed is superreactive to serotonin in comparison with the normal bed. This resetting of reactivity to serotonin is due to the specific vascular structure as well as to an increased 5-HT2 receptor-mediated sensitivity.