The Effect of Endogenous and Exogenous Gonadotrophin‐releasing Hormone on the Prolactin Response to TRH

Abstract

The prolactin response to TRH in a group of patients with Kallmann's syndrome was found to be significantly lower compared to a group of hypergonadotrophic hypogonadal patients. Since levels of testicular products are comparably low in both groups, we hypothesize that high endogenous LHRH production might be associated with an increased prolactin response to TRH. In support of this, we were, indeed, able to establish a positive correlation between the magnitude of the prolactin response to TRH and basal and LHRH-stimulated LH/FSH levels (the latter serving as an index of endogenous LHRH production) in: (1) eugonadal men, (2) men with Kallmann's syndrome, (3) oestrogen-treated agonadal men, (4) men with severely impaired spermatogenesis and, (5) agonadal men. A direct relation between LHRH and the prolactin response to TRH was demonstrated in a group of eugonadal men, the prolactin response to TRH being greater after prolonged LHRH pretreatment. We speculate that an increase of endogenous or exogenous LHRH might be associated with decreased hypothalamic dopamine secretion which could directly increase prolactin synthesis. Indirectly, decreased dopamine secretion could augment the potency of TRH in releasing prolactin.

Evaluation of GnRH administration on the prolactin response to thyrotrophin-releasing hormone in normal women.

“…Our experimental design might exclude these probable effects of an endogenous estrogen level and a repetitive stimulus of TRH. Similar findings were recently reported in nine normal male subjects who also showed augmented PRL release in response to TRH after GnRH infusion for 4 hours (Gooren et al, 1984). These results indicate that exogenous GnRH has a positive effect on the PRL release either indirectly, by increasing the sensitivity of lactotroph to TRH, or directly by stimulating the secretion of PRL, as previously reported (Braund et al, 1984, Van Loon 1978, Yen et al, 1980.…”

“…GnRH levels in Klinefelter's syndrome and primary testicular failure were considered to be high (Plant et al, 1984). Gooren et al (1984) hypothesized that high endogenous GnRH production might be associated with an increased PRL response to TRH by observing a positive correlation between basal as well as GnRH-stimulated gonadotrophin levels and the magnitude of TRH-induced PRL release. These observations suggest that endogenous GnRH levels also might be related positively with a PRL response to TRH as described by Gooren et al (1984).…”

“…These reports clearly indicate that GnRH is one of the numerous substances responsible for stimulating PRL release in humans. Furthermore, the augmenting effect of exogenous GnRH on the release of PRL in response to TRH in men was recently reported (Gooren et al, 1984). This study was designed to investigate the role of GnRH on PRL release in response to exogenous TRH in normal women.…”

Effects of progesterone on prolactin secretion in hypogonadal women.

“…Exogenous GnRH stimulates secretion of prolactin in normal men (Van Loon 1978), normal women (Yen et al, 1980, Braund et al, 1984 and in various pathological conditions (Giampietro et al, 1979, Beumont et al, 1980, Georgitis et al, 1983. Furthermore, Gooren et al (1984) observed the phenomenon that endogenous and exogenous GnRH has a positive effect in releasing prolactin in response to thyrotropinreleasing hormone in men. A similar phenomenon has been observed previously (Spitz et al, 1979).…”

Prolactin Response to TRH Is Unaltered by Pulsatile Infusion of LHRH

“…In the syndrome of isolated gonadotrophin deficiency, both intact and attenuated PRL responses following thyrotro phin-releasing hormone (TRH) have been described [1][2][3][4][5], Recently Gooren et al [6] have reported impaired PRL response to TRH in a group of patients with Kaliman's syndrome when compared with a group of hypergonadotrophic hypogonadal patients with similar serum testosterone concentrations. They postulated a direct re lationship between endogenous lutenizing hormone-re leasing hormone (LHRH) secretion and PRL release.…”