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The influence of exogenous prolactin-induced hyperprolactinaemia and bromocriptine-induced hypoprolactinaemia on LH secretion, endocrine function of testes and the structure of seminiferous tubules was investigated in boars. Treatment with exogenous pig prolactin for 21 days (0.07 mg kg-1 day-1; n = 5) caused a significant increase in mean prolactin concentrations during the experiment (P &lt; 0.05) and during 4 h sampling (P &lt; 0.01). Treatment with bromocriptine (0.2 mg kg-1 per os and 0.05 mg kg-1 i.m.; n = 4) decreased mean prolactin concentrations throughout the experiment as well as during two 4 h sampling periods (P &lt; 0.01). Treatment with exogenous prolactin decreased mean LH concentrations during the treatment (P &lt; 0.01) and during the first 4 h sampling period (P &lt; 0.05), but did not affect the number of pulses, pulse frequency or amplitude. Bromocriptine did not affect LH concentrations. Prolactin increased testosterone concentrations during the treatment (P &lt; 0.01), while boars treated with bromocriptine had lower testosterone concentrations (P &lt; 0.05) than did controls. Both exogenous prolactin and bromocriptine treatments significantly decreased oestradiol concentrations during the course of the experiment. The injections of prolactin and administration of bromocriptine caused a decrease in LH/hCG receptor concentration (P &lt; 0.05) in the cell membrane of testes, without causing a change in binding affinity. The bromocriptine treatment caused premature release of some spermatocytes and the presence of polynucleate cells in the seminiferous tubules. In the seminiferous epithelium of hyperprolactinaemic boars, more mature cells (mainly spermatids) were released into the lumen. In tubules in which many polynucleate cells were found, considerable regression of seminiferous epithelium occurred.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of hypoprolactinaemia and hyperprolactinaemia on LH secretion, endocrine function of testes and structure of seminiferous tubules in boars