Failure of Oxytocin and Lysine-Vasopressin to Stimulate Prolactin Release in Humans

Abstract

In order to test a possible stimulatory effect of oxytocin and lysine-vasopressin on prolactin (PRL) release six female volunteers received either saline or 1 IU oxytocin (Syntocinon) i.v.. Blood sampling was performed at intervals over 90 minutes. Nine puerperae were treated with oral oxytocin (Sandopart) 50 IU t.i.d. for seven days. Nine other untreated postpartum women served as controls. Blood was collected before delivery and on subsequent postpartum days, and the milk volumes produced were estimated by increases in the babies' weight. In addition, seven volunteers received 5 or IU lysine-vasopressin (Vasopressin) i.m. Blood was withdrawn at regular intervals for 180 minutes, the urine volumes excreted in 30-minute intervals were measured and the clearance of free water calculated. Oxytocin failed to modify basal plasma PRL in the acute trial and in the post-partum women, and milk amounts produced were not influenced by treatment. Vasopressin did not change the PRL plasma profile despite a significant (p less than 0.05) reduction in the excretion of free water. Results indicate that neuropeptides are not implicated in the control of PRL release.

The Inability of Oxytocin to Influence the Secretion of Testosterone, Prolactin, Luteinizing and Follicle-Stimulating Hormone in Normal Men

“…In our study we were unable to establish any influence of oxytocin on the plasma levels of prolactin, LII, FSH and testosterone secretion iñ nQrmal male subjects. These findings are consistent with the report of del Pozo et al (1980). In their bolus injection study they showed that oxytocin do not modify basal prolactin levels in female volunteers and in postpartum women.…”

“…Since oxytocin is localised to the external layer of the hypothalamic eminentia mediana, it is likely that it is found in high concentration in portal vessels, as is vasopressin (McCann et al, 1982). The studies in humans demonstrated the inability of exogenous oxytocin to release prolactin (del Pozo et al, 1980). On the contrary, in vivo animal studies suggested that it stimulates prolactin secretion (Lumpkin et al, 1983).…”

Enkephalins and Endorphins

“…side effects in man; oppression of chest, red eyes, whole body flushing, as well as a flare reaction with intradermal injection (Von Grafferied et al, 1978). In addition, FK 33-834 increased PRL and GH and reduced cortisol (del Pozo et al, 1980). The present study supports and extends the original findings by Golstein et al, (1981) that methionine enkephalin can be administered safely to man over a wide range.…”

Enhancement of the GH responsiveness to GH releasing stimuli by lysine vasopressin in type 1 diabetic subjects

“…It is well known that posterior pituitary hormones may influence anterior pituitary function in humans. However, these hormonal actions appear to be specific; for example, the administration of lysine vasopressin (LVP) significantly stimulates ACTH ( Gwinup et al ., 1967 ; Brostoff et al ., 1968 ; Cavagnini et al ., 1976 ; Legros et al ., 1982 ) and GH secretion ( Brostoff et al ., 1968 ; Chiodera & Coira, 1985; Coiro et al ., 1985 ), whereas it does not change FSH, LH ( Chiodera et al ., 1987 ), TSH and PRL ( del Pozo et al ., 1980 ; Chiodera et al ., 1988 ) secretions in basal conditions. Furthermore, LVP is unable to modify the LH‐RH‐induced gonadotrophin rise ( Chiodera et al ., 1987 ) and the TSH and PRL responses to TRH ( Chiodera et al ., 1988 ).…”