Polyamines, vitamin D, and intestinal cells

Abstract

Earlier, this group of investigators reported that duodenal ornithine decarboxylase activity and the tissue content of putrescine was found to be increased markedly after a single intravenous injection of 1,25(QH)zD, into vitamin D-deficient chicks (Biochem J 1981;195:685-90). Of interest, however, in this regard was the subsequent finding by these investigators that prior administration of a-difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase, did not suppress the increase in putrescine levels in intestine by 1,25(OH),Ds. Thjs latter result suggested that the so-called “reverse pathway” for the synthesis of putrescine from spermine or spermidine, or both, might be involved in the 1,25(OH)zDs effect on putrescine levels. Therefore, in the present study, these investigators, using the same experimental system, examined the effect of 1,25(OH),D, on the activity of duodenal spermidine N’-acetyltransferase, a rate-limiting enzyme catalyzing the conversion of spermidine to putrescine. The latter enzymatic activity was found to increase within 30 min after a single injection of 625 ng of l,25(OH)2D3 apd attained a maximum level at 2 h. As little as 1.25 ng of 1,25(OH)2Ds induced a small but significant increase in enzymatic activity and the maximum response was seen with 125 ng of the vitamin. Furthermore, the dose of this hormone required to induce duodenal spermidine Nl-acetyltransferase activity was only one-tenth as much as that required to induce ornithine decarboxylase activity. Moreover, the former enzymatic activity was induced in several of the target tissues of vitamin D, whereas, ornithine decarboxylase activity was increased by the vitamin only in the intestine. Because certain target tissues do not appear to be involved in the regulation of mineral metabolism, these authors suggested that the increment of cellular putrescine induced by 1,25(OH)zDs was most likely related to cellular growth or differentiation, or both.