Parathyroid hormone raises the Pi concentration in a cultured osteoblast model.

After feeding of rats with the raw soyabean diet, serum polyamine concentrations (primarily spermidine) were significantly increased at 6 and 12 h (Table I ) . N o similar increases were apparent in the control animals. After 24 h, the circulating levels of polyamines returned to control values and subsequently the total polyamine content in the blood was below normal. These later changes suggest that clearance of polyamines from the circulation occurred at higher rates in soyabean-fed rats than in controls. In another experiment, feeding of rats (7 g/day per rat) for 7 days with a lactalbumin-based diet containing purified trypsin inhibitors (28 g/kg diet) resulted in a considerable increase in pancreatic dry weight ( + 82 f 14 mg) and polyamine content ( + 1345 f 350 nmol/pancreas) compared with that obtained for controls. The lectin (7 g/kg diet) had a similar effect upon pancreatic weight ( + 60 k 14 mg) and polyamine content ( + 928 f 179 nmol/pancreas). The control values for pancreatic dry weight were 158 f 14 mg and for polyamine content 2209 f 179 nmol/pancreas. Treatment of rats with 12001300 mg/day per kg rat body weight of a-difluoromethylornithine (DFMO), an irreversible inhibitor of ODC [5], lowered pancreatic activity of ODC in test and control groups from 3.0 k 0.5 to 1 .Of 0.5 nmol of putrescinc/h per pancreas. However. it did not reduce pancreatic polyamine accumulation or growth induced by the trypsin inhibitors or the lectin. Therefore, it appears that most of the additional polyamines found in the pancreata of rats fed with soyabean. trypsin inhibitors o r lectin were not synthesized de m v o . Pancreatic activity o f spcrmidinc/spermine W-acetyltransferase (SAT) 161 was high (25 f 9 nmol o f N1-acetylspermidine/h per pancreas). Thus, much of the required polyamines could have been generated in the pancreas via the interconversion pathway if they were available from the circulation. However, since SAT activity was not significantly increased by feeding of rats with soyabean, trypsin inhibitors or lectin, accumulation of polyamines could only occur if the rate of uptake of polyamines from circulation into the pancreas was higher in these rats than in controls. This would be consistent with the elevated rates of polyamine clearance from thc circulation found in soyabean-fed rats (Table I ) and in accordance with the finding [ 71 that dietary kidncy bean lectin could stimulate the uptake o f "C-labelled polyamines by the pancreas. Since luminally applied polyamines are rapidly taken up systemically [ 8 ] and the raw soyabean protein diet contained 4 10 f 16 nmol of total polyamines (primarily spermidine)/g of diet. it is possible that the high levels of circulating polyarnines at 6 and 12 h after exposure to soyabean and the polyamines subsequently accumulated in the pancreata (Table 1) could have originated indirectly from these luminally supplied polyamines. However, the semi-synthetic diets used in the studies with the purified trypsin inhibitors and lectin contained < 0.5 nmol of total polyamines/g. The required polyamines could not, therefore, have been supplied through the diet and were probably derived from either bacterial [Y, 101 or systemic sources. Thus, the high serum polyarnine concentrations observed at 6 and 12 h in soyabean-fed rats may have, in part, been due t o release of stored polyamines in response to the higher requirements o f the pancreas for polyamines.