Effects of hypophysectomy on purinergic and noradrenergic contractility of the rat vas deferens

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Abstract
1. The effects of removal of the pituitary on vas deferens contractile function were examined in young adult male rats having undergone hypophysectomy 7 days previously. Sham-operated age-matched rats served as controls. Responses to electrical field stimulation (EFS), and exogenous noradrenaline (NA) and beta, gamma-methylene ATP (beta, gamma-meATP) were tested. 2. Hypophysectomized rats lost weight over the 7 days. Body weights were 267.2 +/- 3.9 g (n = 7) in controls and 195.3 +/- 1.56 g (n = 5) with hypophysectomy. The wet weight of the vas deferens from rats with hypophysectomy, 22.8 +/- 1.8 mg (n = 5) was approximately half that of the controls, 41.3 +/- 1.2 mg (n = 7). The contractile response to KCl was smaller in hypophysectomized preparations (0.97 +/- 0.9 g, n = 5) than in controls (2.91 +/- 0.2 g, n = 7). 3. The alpha 1-adrenoceptor antagonist prazosin (1 microM) was more effective as an inhibitor of the tonic than of the twitch component of the contractile response, indicating a dominant adrenergic component. However, alpha, beta-methylene ATP was also effective at inhibiting the tonic component, indicating that ATP is also released secondarily to NA. 4. Absolute contractions to EFS of vas deferens from hypophysectomized rats were smaller than those of the controls; however, when corrected for the difference in smooth muscle function (expressed as a percentage of the contraction to 120 mM KCl), the twitch response was significantly greater than in the controls at frequencies of up to 16 Hz, maximal responses being unaffected. In contrast, the tonic response was not significantly different between the two groups. 5. The sensitivity of contractions evoked by NA (1-300 microM) was less in vas deferens from hypophysectomized rats than in the controls. 6. Contractions of the vas deferens to beta, gamma-meATP (1-300 microM) were greater in hypophysectomized rats than in the controls. 7. In conclusion, the present results indicate that hypophysectomy of rats causes an increase in the twitch, but not the tonic component of the vas deferens contractile response to EFS. This appears to be due to an increase in the number or sensitivity of postjunctional P2X-purinoceptors, there being a reduction in sensitivity to NA.