Abstract
The effects of morphine on the hypothalamic-pituitary axis were examined in the male rat. Both acute and chronic morphine administration significantly lowered serum luteinizing hormone (LH) levels and, subsequently, testosterone. The locus of action of morphine seems to be at the level of the hypothalamus since it was found that: acute morphine treatment did not alter the content of LH in the pituitary, whereas chronic administration increased the levels slightly (these data suggest that the synthesis of LH is probably not blocked by the narcotic); morphine alone has no direct effect on base-line (nonstimulated) release rates of LH from the pituitary; morphine did not block the effects of luteinizing hormone releasing factor on the secretion of LH by the pituitary, in vivo or in vitro; and morphine markedly reduced the increase in serum LH levels produced by castration in the male rat. Since castration increases serum LH levels by releasing testosterone's feedback control of the hypothalamic mechanisms involved in the secretion of LH, the present results suggest that morphine blocks the increase in the activity induced by castration in these hypothalamic pathways. The foregoing observations, therefore, implicate the hypothalamus as the site of the disruptive action of the narcotic on reproductive endocrinology. Moreover, the observations additionally suggest that the secretion and/or synthesis of luteinizing hormone releasing factor is impaired in morphine-treated animals.
Original language | English |
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Pages (from-to) | 548-555 |
Number of pages | 8 |
Journal | Unknown Journal |
Volume | 203 |
Issue number | 3 |
State | Published - 1977 |
Externally published | Yes |