An investigation of the effectiveness of testosterone implants in combination with the prolactin inhibitor quinagolide in the suppression of spermatogenesis in men

BACKGROUND: Administration of testosterone inhibits gonadotrophin secretion and spermatogenesis in men but the degree of response is highly variable. This treatment also stimulates prolactin, itself a progonadal hormone in animals. This study investigated whether concomitant suppression of prolactin (PRL) with the non-ergot, dopamine receptor agonist quinagolide (Q), would enhance the efficacy of testosterone in its inhibition of spermatogenesis in healthy eugonadal men. METHODS: A total of 46 men were randomized to three treatment groups: Group 1, T1200: 1200 mg testosterone implant plus daily oral placebo; Group 2, T1200 + Q: 1200 mg testosterone plus oral Q 75 microg/day; Group 3, T800 + Q: testosterone 800 mg plus oral Q 75 microg/day. After an initial pre-treatment period of 4 weeks, subjects were treated for 24 weeks followed by an 8-week recovery period. RESULTS: The total numbers of subjects that achieved severe oligospermia (< or =10(6)/ml including azoospermia) from weeks 8-16 were 11/13 (85%), 11/12 (92%), 8/13 (61.5%) in the three groups respectively. CONCLUSIONS: The results show that inhibition of PRL does not to confer additional efficacy in spermatogenic suppression in men. However, Q did not totally block PRL secretion in the subjects, possibly because testosterone replacement itself stimulated PRL by a direct action on the lactotroph, thus the effectiveness of dual inhibition of gonadotrophin and PRL could not be fully investigated.