Endogenous prolactin modulated the calcium absorption in the jejunum of suckling rats

Abstract

Prolactin has been reported to stimulate intestinal calcium absorption in young and mature, but not aging rats. The present study was performed on suckling rats to elucidate the actions of endogenous prolactin on calcium absorption in various intestinal segments. Before measuring the calcium fluxes, 9-day-old rats were administered for 7 days with 0.9% NaCl, s.c. (control), 3 mg/kg bromocriptine, i.p., twice daily to abolish secretion of endogenous prolactin, or bromocriptine plus exogenous 2.5 mg/kg prolactin, s.c. Thereafter, the 16-day-old rats were experimented upon by instilling the 45Ca-containing solution into the intestinal segments. The results showed that, under a physiological condition, the jejunum had the highest rate of calcium absorption compared with other segments (1.4 +/- 0.35 micromol.h-1.cm-1, p < 0.05). The duodenum and ileum also manifested calcium absorption, whereas the colon showed calcium secretion. Lack of endogenous prolactin decreased lumen-to-plasma and net calcium fluxes in jejunum from 2.07 +/- 0.31 to 1.19 +/- 0.12 and 1.40 +/- 0.35 to 0.88 +/- 0.18 micromol.h-1.cm-1 (p < 0.05), respectively, and exogenous prolactin restored the jejunal calcium absorption to the control value. Endogenous prolactin also had an effect on the duodenum but, in this case, exogenous prolactin did not reverse the effect of bromocriptine. However, neither ileal nor colonic calcium fluxes were influenced by prolactin. Because luminal sodium concentration has been demonstrated to affect calcium absorption in mature rats, the effect of varying luminal sodium concentrations on calcium fluxes in suckling rats was evaluated. The jejunum was used due to its highest rate of calcium absorption. After filling the jejunal segments with 124 (control), 80, 40 mmol/L Na+-containing or Na+-free solution, increases in calcium absorption were found to be inversely related to luminal sodium concentrations in both control and bromocriptine-treated rats. The plasma concentration of 45Ca under luminal sodium free condition was also higher than that of the control condition (2.26% +/- 0.07% vs. 2.01% +/- 0.09% administered dose, p < 0.05). However, 3H-mannitol, a marker of the widening of tight junction that was introduced into the lumen, had a stable level in the plasma during an increase in plasma 45Ca, suggesting that the widening of tight junction was not required for enhanced calcium absorption. In conclusion, calcium absorption in suckling rats was of the highest rate in the jejunum where endogenous prolactin modulated calcium absorption without increasing the paracellular transport of mannitol.

Prolactin is an important regulator of intestinal calcium transport

“…Besides being an important regulator of intestinal calcium transport during pregnancy and lactation, prolactin also regulates calcium absorption in mammals during the neonatal period (Amnattanakul et al 2005). In suckling rats, sources of plasma prolactin are both endogenous of pituitary origin and exogenous of milk origin (approx.…”

Intestinal absorption and renal reabsorption of calcium throughout postnatal development

“…Under conditions where only exogenous prolactin was present, net calcium absorption from the duodenum was absent. 55 This study illustrates the potential for endogenous and exogenous prolactin to confer different effects on intestinal calcium absorption. In adult mice and in human cell culture models, endogenous prolactin appears to increase calcium flux through an L-type calcium channel, presumably Ca v 1.3.…”

“…The jejunum appeared to be the segment of greatest net absorption which increased when luminal sodium decreased, independent of mannitol flux. 55 Thus, limited evidence supports transcellular calcium absorption from the distal small intestine prior to weaning. This is in contrast to net secretion from the jejunum and net absorption in the cecum in adult rodents.…”

High Physiological Prolactin Induced by Pituitary Transplantation Decreases BMD and BMC in the Femoral Metaphysis, but Not in the Diaphysis of Adult Female Rats

“…By regulating calcium mobilization in these target organs during pregnancy and lactation, the high physiological PRL of 75-300 ng/ ml increases calcium availability for fetal growth and milk production [4]. Moreover, the basal PRL level of 7-10 ng/ ml was required for the maintenance of normal bone turnover and duodenal calcium absorption in rats [5,6].It has been shown that PRL acted directly on the intestinal absorptive cells to enhance calcium absorption [3]. In bone, osteoblasts but not osteoclasts strongly expressed functional PRL receptors (PRLR), indicating that bone was also a target of PRL [7].…”

“…By regulating calcium mobilization in these target organs during pregnancy and lactation, the high physiological PRL of 75-300 ng/ ml increases calcium availability for fetal growth and milk production [4]. Moreover, the basal PRL level of 7-10 ng/ ml was required for the maintenance of normal bone turnover and duodenal calcium absorption in rats [5,6].…”