Suckling in lactating women stimulates the secretion of insulin and prolactin without concomitant effects on gastrin, growth hormone, calcitonin, vasopressin or catecholamines (original) (raw)
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Milk-borne hormones: possible tools of communication between mother and suckling
Physiological research / Academia Scientiarum Bohemoslovaca, 1995
Early studies suggested endocrine type mother-pup interaction: 131I administered to suckling rats appeared via the urine of the suckling and mother's milk in the circulation of litter mates who were not injected with iodine; levels of thyroxin in rat milk were influenced by the status of the thyroid gland of the lactating rat. Administration of TRH (thyrotropin releasing hormone) to lactating mothers led to an appearance of unaltered hormones in the milk and stomach content of sucklings. TSH (thyroid stimulating hormone) or ACTH (adrenocorticotropic hormone) when given orogastrically to suckling rats increased thyroid hormones and corticosterone serum levels in suckling rats. Functional effects of gastrointestinal administration of insulin, bombesin (mammalian analog of gastrin-releasing peptide) and epidermal growth factor (EGF) are reviewed in detail (32 references).
Asia-Oceania journal of obstetrics and gynaecology / AOFOG, 1994
Prolactin response to suckling was studied in a group of fully breast feeding women (N = 58) between 4-6 weeks postpartum. Basal, suckling stimulated and the increment of prolactin showed wide individual variations. Basal prolactin concentrations varied from 140 to 4,600 mIU/l, suckling stimulated prolactin from 400 to 5,600 mIU/l and the increment of prolactin from 40 to 4,160 mIU/l. Basal (p = 0.0395) and suckling stimulated (p = 0.0423) prolactin concentrations significantly increased as the number of night breast feeds increased and the suckling stimulated (p = 0.0218) prolactin concentrations significantly increased as the number of breast feeds/24 h increased. However, the magnitude of the rise in prolactin in response to suckling was not dependent on basal prolactin concentration. Basal, suckling stimulated or the increment of prolactin were not significantly different between subjects having different breast feeding frequencies, when the subjects were grouped according to th...
Physiology & Behavior, 2001
Previous work has shown that physiologic activation of the sympathetic system may inhibit milk yield (ME) in rats. Thus, adrenal catecholamines (CAs) are released by suckling, but it is not known whether such inhibition results also from reflex activation by the same stimulus of neural sympathetics upon the mammary gland. The present experiments were designed to determine whether suckling inhibits ME induced by oxytocin (OT) in the urethane-anesthetized lactating rat, and whether such inhibition results from adrenal and/or neurally released CAs. Rats were isolated (6 h) from their pups and then anesthetized. OT (0.8 mU every 2 min) was administered intravenously to the mothers during suckling. Rats were either chronically implanted with cannulae into the lateral cerebral ventricles (intracerebroventricularly), bilaterally adrenalectomized (ADX), hypophysectomized (HX), spinal cord transected (SCT: T3 -T4), or had the nipple area (NA) locally anesthetized before suckling. MEs were low in control, sham, ADX and HX rats, but not in rats given the b-adrenergic blocker propranolol (PROP; intravenously or intracerebroventricularly injected), nor in SCT, NA or PROP-HX rats. As revealed by ductal resistance measurements as an indicator of ductal tone, suckling-induced inhibition of ME was due to ductal constriction within the mammary glands. These effects of suckling, however, could be prevented by prior activation of ductal mechanoreceptors. Together, these results indicate that suckling inhibits ME through the reflex activation of neurally mediated central b-adrenergic mechanisms, and that these effects, in turn, can be regulated by ductal mechanoreceptor activation. D
β-Adrenergic mechanisms modulate central nervous system effects of prolactin on milk ejection
Physiology & Behavior, 2001
It is known that prolactin (PRL) is produced within the brain and numerous central actions of the hormone have been reported. In anesthetized lactating rats, central administration of PRL, i.e., intracerebroventricular (icv) or intrathecally (it), facilitated milk ejection (ME) by depressing the sympathetically mediated facilitatory tone of the mammary ductal system. However, it is not known whether or not the same effects and similar mechanisms take place in conscious rats after PRL administration. In the present study, the effects of centrally administered PRL, i.e., icv or it, on ME was determined in both conscious and anesthetized rats. In conscious rats, the rate of ME was determined by applying a 15-min period of suckling by the litter, following a 6-h period of isolation. In anesthetized rats, intramammary pressure (IMP) responses of the mammary glands to exogenous oxytocin (OT) were recorded. The results showed that, whereas in anesthetized rats, increased responsiveness of the mammary glands to OT were observed after PRL administration, an intense inhibition of ME occurred in conscious rats. Because, in conscious and anesthetized rats, these effects were prevented by prior administration of the badrenergic blocker propranolol (PROP) to the mothers, this suggests that the PRL effects on ME are modulated through sympathomimetic and sympatholytic actions in conscious and anesthetized rats, respectively. Thus, as shown by ductal tone measurements, in conscious, but not in anesthetized rats, the effect of PRL was associated with increased ductal constriction within the mammary glands; an effect that was mimicked by icv administration of the b-adrenergic agonist isoproterenol (ISOP) and that was prevented by PROP. Further, the sympatholytic action of icv-PRL in anesthetized rats prevented the effect on ductal tone of both icv-PRL in conscious rats and of ISOP in anesthetized rats. Taken together, these results clearly suggest that the central effects of PRL on ME are modulated by adrenergic mechanisms.
Prolactin and insulin levels in lactating sows in relation to nursing frequency☆
It has been established that sows up-or down-regulate their milk production as the frequency of nursings is changed. The amount of udder massage by piglets might also influence milk production. To investigate whether these effects are associated with changes in prolactin or insulin levels, we enforced five sows each to nurse either every 35 min (MIN35) or every 70 min (MIN70) over a 26-to 28-hr period. Milk production was measured during the first 24 hr of this period. During the last three to four nursings, blood was collected every 5 min. Plasma prolactin levels increased after milk ejection (P Ͻ 0.05), whereas insulin levels increased only briefly in MIN70 sows. Sows nursing every 35 min had lower basal (P Ͻ 0.001) and maximal (P Ͻ 0.05) concentrations of insulin than MIN70 sows. There were no differences between the two groups in prolactin levels. Nursings with a postejection udder massage longer than 90 s tended to induce a higher increase in prolactin (P Ͻ 0.1) than nursings with a shorter massage. When the effects of imposed nursing frequency were removed, there was an across-sows positive residual correlation between average prolactin levels (P Ͻ 0.05) and the duration of post-ejection udder massage during the preceding 24 hr. We conclude that when milk production of a sow is changed by altering the nursing frequency within natural limits, the necessary alteration in catabolic state of energy metabolism may be associated with altered insulin levels. The duration of udder massage in ૾ This work was supported by the following grants from the Grant Agency of the Czech Republic: No. 523/98/0789 to M.Š ., No. 523/99/0985 to G.I., and No.523/99/0603 to P.K. a single nursing might have only a slight immediate impact on prolactin levels, but may influence prolactin levels more substantially if increased for a period of 24 hr.
Stimulation of Anterior Pituitary Galanin and Prolactin Gene Expression in Suckling Rats
Endocrine, 1999
Galanin and PRL Expression in Suckling Rats/Ren et al. Recent evidence suggests that galanin may regulate prolactin (PRL) secretion during lactation. In this article, we describe the regulation of anterior pituitary galanin and PRL gene expression during pregnancy and after parturition in the rat. Expression of galanin and PRL in the anterior pituitary were significantly higher at d 20 of pregnancy compared to diestrus. One day after parturition, galanin mRNA levels increased a further 4.5-fold. This post partum increase in gene expression was not observed for PRL. The increase in galanin gene expression was maintained above the diestrous level for at least 10 d after parturition. PRL mRNA expression, on the other hand, was largely unchanged after parturition. Although the increase in galanin gene expression 1 d after parturition was independent of suckling, subsequently, galanin gene expression was significantly higher in nursing mothers. Anterior pituitary galanin gene expression was 12-fold higher in nursing mothers compared with those that were not, 3 d after parturition. Similarly, PRL gene expression was significantly lower in mothers who were not suckling their pups 3 d after parturition. Initiation of suckling alone was insufficient to stimulate galanin and PRL expression. Despite suckling for 2 d, removal of the suckling stimulus subsequently resulted in a rapid decrease in galanin gene expression. Hence, the stimulatory effect of suckling on galanin expression requires a sustained suckling stimulus. In conclusion, the data support the hypothesis that anterior pituitary galanin plays an important role during lactation, likely acting to amplify lactotroph stimulation through paracrine and autocrine mechanisms.
Hypothalamo-pituitary portal blood concentrations of -endorphin during suckling in the ewe
Reproduction, 1987
Matched hypothalamo\p=n-\pituitaryportal and jugular blood samples were collected over about 6 h from 7 lactating Corriedale ewes penned with their lambs, and a careful record was kept of ewe/lamb behaviour. Hypothalamo\p=n-\pituitaryportal blood concentrations of \g=b\-endorphin were measured by radioimmunoassay and the secretion rates were calculated; these were related to peripheral plasma prolactin and LH concentrations, and the sucking bouts of the lambs. Basal LH concentrations remained <1 ng/ml with 0\p=n-\2 pulses of 1\ m=. \ 5\ p=n-\ 3\ m=. \ 5 ng/ml amplitude per 6-h collection period. Prolactin secretion was episodic with individual baselines varying from 24 to 286 ng/ml, and peak concentrations of 50\p=n-\631 ng/ml. Portal \g=b\-endorphin was secreted in an episodic pattern with individual baseline secretion rates varying from 0\m=.\125to 0\m=.\495 ng/min, and peak secretion rates of 0\m=.\768to 3\m=.\216 ng/min. A close correlation was seen between sucking bouts and the secretion of portal \g=b\-endorphin and peripheral prolactin; 86% of sucking bouts resulted in a significant release of \g=b\-endorphin, and 46% of sucking bouts resulted in a significant release of prolactin. These results show that hypothalamic \g=b\-endorphin is released in response to the sucking stimulus. This provides support for the hypothesis that, during lactation, \g=b\-endorphin acts within the hypothalamus to reduce GnRH release and hence depress pituitary gonadotrophin secretion.
Biological Research For Nursing, 2009
The present study was designed to compare milk production and hormone responses (prolactin [PRL], oxytocin [OT]) and to determine associations of hormone levels with milk production in mothers of preterm (PT) and term (TM) infants during the first 6 weeks postpartum. Mothers of PT infants (n ¼ 95) were all pump dependent; mothers of TM infants (n ¼ 98) were all feeding their infant at breast. Mothers of nonnursing PT infants produced less milk over time compared to mothers of TM infants. A higher proportion of PT mothers had lower basal PRL levels compared with TM mothers. PRL and frequency of breast stimulation combined positively influenced milk production in PT mothers. OT levels were higher in PT versus TM mothers, but OT was not related to milk production. Further study is warranted regarding interventions to enhance milk production, particularly in pump-dependent mothers of PT infants.