3. After addition of 5 mm theophylline, the [Ca2+]i in enterocytes from con-piglets doubled during the 10 min incubation. This effect, however, was three times higher in enterocytes from def-piglets compared with those from con-piglets. Similar results were obtained after 4 min incubation of enterocytes from con-and def-piglets in the presence of 1 /UM ionomycin. In preparations from def-D3-piglets, ionomycin-induced increases in [Ca2+]iwere significantly lower compared with enterocytes from def-piglets and were not different from the control values. 4. From the results, substantial support is given for the hypothesis that one of the major functions of mucosal calbindin-DAk is the effective buffering of Ca2+ ions.

SUMMARY1. Active sodium (Na+) and chloride (Cl-) 5. Blocking Ca2+ entry into the cytosol by adding either 0-1 mM-TMB-8 or 0-5 mMd,l-verapamil to the serosal bathing solution abolished the difference in ISC response to theophylline between indomethacin-treated LC and NC mucosa due to greater depression of I., in LC than in NC mucosa.6. The combined effects of theophylline and A23187 on ISC stimulation were calcitriol dependent. In the presence of indomethacin this dependence was only significant when A23187 was given prior to theophylline. In the absence of indomethacin the combined effects of A23187 and theophylline on ISC were always significantly greater in LC than in NC mucosa, irrespective of the order of adding the two agents.7. Addition of theophylline stimulated net Na+ and Cl-secretion in indomethacintreated LC and NC mucosa. The increases of net Na+ and Cl-fluxes fully accounted for the rise of ISC with NC mucosa but accounted only partly for the increase in I., with LC mucosa. This resulted in significant increase in theophylline-stimulated MS 8176 15-2 B. SCHRODER, R. KA UNE AND J. HARMEYER residual ion flux (JR) in LC mucosa which probably resulted from enhanced secretion of bicarbonate.8. The experiments showed that in pig jejunal mucosa stimulation of ISC and ion transport by theophylline requires Ca2 . Greater stimulation of ISC in LC mucosa than in NC mucosa is explained by assuming a lower cytosolic Ca2+-buffering capacity. This probably resulted from the lower calbindin concentration in LC mucosa.9. The study shows that calcitriol alters responsiveness of the jejunal mucosa to Ca2+-dependent secretory stimuli.

The role of 1,25-dihydroxycholecalciferol (calcitriol) for intestinal calcium (Ca2+) absorption was studied in newborn (< 1 week old) and weaned piglets (> 6 weeks old). In both groups, normal piglets and piglets suffering from inherited pseudo vitamin D-deficiency rickets, type I (PVDRI) were used. In this inherited disorder, renal production of calcitriol is absent. Plasma samples were assayed for calcitriol and total Ca, and dissociation constants (Kd) and maximum binding capacities (Bmax) of intestinal calcitriol receptors were determined under equilibrium conditions at 4 degrees C. Unidirectional Ca(2+)-flux rates were measured across stripped duodenal mucosae in Ussing chambers in the absence of electrochemical gradients. The plasma calcitriol concentrations of neonatal (26.5 +/- 7.1 pg/ml, n = 11; mean +/- SEM) and weaned PVDRI piglets (18.8 +/- 5.7 pg/ml, n = 8) were unphysiologically low and differed significantly from control animals (83.6 +/- 14.8 pg/ml, n = 8, and 86.9 +/- 9.6 pg/ml, n = 11, respectively). However, newborn PVDRI piglets had normal plasma Ca levels at least during the first days of life. They became hypocalcemic and developed clinical symptoms of rickets during the following weeks. In newborn PVDRI and control piglets, Bmax was significantly lower (84 +/- 28 fmol/mg protein and 127 +/- 55 fmol/mg protein, n = 9, respectively) than in weaned piglets (741 +/- 82 fmol/mg protein, n = 9, and 778 +/- 121 fmol/mg protein, n = 8, respectively). Significant net Ca(2+)-fluxes were found in both newborn PVDRI and control piglets (88.8 +/- 25.1 nmol.cm-2 x h-1, n = 6, and 86.5 +/- 10.5 nmol.cm-2 x h-1, n = 9, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Abstract. Vitamin D metabolism was studied in the 'Hannover Pig', a strain which suffers from pseudo vitamin D-deficiency rickets, type I. Animals of this strain are known to be devoid of renal 25-hydroxyvitamin D3-1α-hydroxylase and -24-hydroxylase activities. Pigs with florid rickets and hypocalcaemia were treated with single im injections of 0.25 to 1.25 mg of vitamin D3, doses that have been shown in previous studies to be effective in producing transient healing of rachitic symptoms. The levels of vitamin D3 and its most relevant physiological metabolites in plasma were estimated at intervals before and after this vitamin D3 treatment. Vitamin D3 rose from 14.8 ± 8.1 to 364 ± 190 nmol/l (mean ± sd) 2 to 3 days post injectionem, 25-hydroxyvitamin D3 from 131.0 ± 46.2 to 1068 ± 160 nmol/l within 7 days post injectionem. The 1α,25-dihydroxyvitamin D3 concentration in plasma was elevated from 73.9 ± 25.0 to 281 ± 168 pmol/l 2 to 3 days post injectionem and declined continually from that time. 24R,25-dihydroxyvitamin D3 and 25S,26-dihydroxyvitamin D3 levels after treatment showed different responses in different animals being either elevated or unchanged. Clinical healing of the pigs with these doses of vitamin D3 was attributed to the transient rise of 1α,25-dihydroxyvitamin D3 in plasma. It was assumed that 1α,25-dihydroxyvitamin D3 synthesis takes place under these circumstances in extrarenal tissues.

SUMMARY1. Na-Pi co-transport was analysed using renal cortical and small intestinal brush-border membrane vesicles which were isolated from control (normal, heterozygotes) and rachitic piglets (homozygotes).2. A kinetic analysis of Na-dependent initial linear uptake of Pi was performed using vesicles obtained from control animals. The results suggest similar kinetic properties for the renal and small intestinal co-transport system. (i) A sigmoidal dependence on Na concentration of Pi uptake suggests the involvement of more than one Na ion in the co-transport. (ii) Increasing Na concentration leads to an increase in the apparent affinity of the transport system for Pi and has minimal effect on the apparent Vmax (maximum velocity of uptake). (iii) Increasing pH leads to an increase in Pi transport rate.3. The kinetic characteristics of the Na-Pi co-transport system in vesicles obtained from rachitic animals were similar to those in controls. The apparent Vmax, but not the apparent Km (Michaelis constant) for Na and Pi, is reduced in intestinal and renal brush-border membranes isolated from rachitic animals as compared to control animals. Injection of vitamin D3, three days prior to killing of rachitic litter-mates, increased the Na-Pi uptake rate in the brush-border membrane vesicles isolated from these piglets. 4. It is concluded that intestinal and renal brush-border membranes from piglets contain a similar Na-Pi co-transport system and that in vitamin-D-dependent rickets the number of operating transport units is reduced in both membranes.

Alcian blue (AB) was applied intravenously to cannulated, conscious Prussian carp. The glomeruli exhibited selective staining with AB. Electronmicroscopy of the filtration barrier revealed dense deposits of AB in the epithelial and endothelial cell coats and in the glomerular basement membrane.The total number of stained glomeruli per kidney was 14,170+578 in flesh water carp, and 6,437 + 2,114 in carp-adapting to isotonic saltwater (ff + SEM). The number of stained glomeruli can be correlated with the urine flow (r=0.79, n= 10,

No abstract

No abstract