# VITAMIN D AND CALCIUM DURING PREGNANCY AND LACTATION

> **NIH NIH R01** · UNIV OF NORTH CAROLINA CHAPEL HILL · 1994 · $158,645

## Abstract

The long-term objectives of this project are to elucidate the mechanisms
involved in the adaptation of calcium (Ca) metabolism to the increased Ca
demands of reproduction and the neonatal period.  Past results have already
stimulated clinical studies on the changes in the circulating concentration
of the Ca regulating hormones in lactating women, as well as studies on
intestinal Ca absorption in very low-birthweight infants.  Future studies
should be similarly provocative.  Specific aims concerning the regulation
of intestinal Ca absorption during reproduction include the identification
of factors responsible for the periparturient peak of duodenal active Ca
transport between 20 days of pregnancy and day 4 of lactation in rats.  The
potential role of 1,25-(OH)2D3, prolactin, placental lactogen-II, estrogen,
or parathyroid hormone-related peptide (PTHrP) will be evaluated by varying
the serum levels of these hormones in pregnant rats.  Changes in the Ca
transport ratio (serosal/mucosal, using everted gut sacs), the
concentration of duodenal calbindin-D9k and its messenger RNA, and the
duodenal 1,25-(OH)2D3 receptor will be measured.  Nonsaturable Ca
absorption in the jejunum and ileum will be determined during the
periparturient period, in order to extend our earlier work indicating
enhanced efficiency of nonsaturable calcium absorption in late lactation.
Specific aims regarding regulation of parathyroid hormone (PTH) secretion
during lactation will include elucidating why superphysiolgic serum Ca
levels do not suppress serum PTH levels of lactating rats to the same
extent as in nonlactating rats.  A bone cell CAMP bioassay will be used to
study the pattern of Ca suppression of PTH release from dispersed rat
parathyroid cells, and to determine if there is a unique (relationship
between extracellular and intracellular Ca concentrations in lactating
rats, perhaps due to an action of corticosterone, which circulates at high
levels during lactation.  Specific aims on regulation of synthesis of
1,25-(OH)2D3 in lactating and suckling rats include determining if the rise
in circulating 1,25-(OH)2D3 levels at the end of pregnancy and the fall at
1-2 days of lactation are caused by parallel changes the rate of renal
biosynthesis of the hormone as determined by the activity of the renal
25-OHD-1-OHase, and if the pregnancy-related increase could be due to an
effect of hypocalcemia, PTH, placental lactogen-II or estrogen on the 1
-OHase, or to an increase in placental 25-OHD-1-OHase that may be
stimulated by parathyroid hormone-related peptide (PTHrP).  Experiments
will also reveal if extrarenal synthesis of 1,25-(OH)2D3 occurs in
lactation, perhaps by the mammary gland in response to a paracrine action
of PTHRP.

## Key facts

- **NIH application ID:** 2196912
- **Project number:** 5R01HD012496-12
- **Recipient organization:** UNIV OF NORTH CAROLINA CHAPEL HILL
- **SAM.gov UEI:** D3LHU66KBLD5
- **Principal Investigator:** SVEIN U TOVERUD
- **Activity code:** R01 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 1994
- **Award amount:** $158,645
- **Award type:** 5
- **Project period:** 1980-04-01 → 1996-02-28

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/2196912

## Citation

> US National Institutes of Health, RePORTER application 2196912, VITAMIN D AND CALCIUM DURING PREGNANCY AND LACTATION (5R01HD012496-12). Retrieved via MORVS 2026-10-25 from https://api.morvs.ai/grant/nih/2196912. Licensed CC0.

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