Ergocalciferol absorption

Using the Woodward-Fieser rules, we can predict the absorption maximum of an unsaturated compound with pleasing accuracy, generally to within 5 nm of the observed value. For example, the calculated absorbance maximum of ergocalciferol (vitamin D2) of 265 nm (Figure 2.8) is only 1 nm different from the observed value at 266 nm (Figure 2.9). 

Figure 2.8 Ergocalciferol (vitamin D2) and the calculated absorption maximum...

As a brief introductory summary, vitamin D substances perform the following fundamental physiological functions (1) promote normal growth (via bone growth) (2) enhance calcium and phosphorus absorption from the intestine (3) serve to prevent rickets (4) increase tubular phosphorus reabsorpiion (5) increase citrate blood levels (6) maintain and activate alkaline phosphatase m bone (7) maintain serum calcium and phosphorus levels. A deficiency of D substances may be manifested in the form of rickets, osteomalacia, and hypoparathyroidism. Vitamin D substances are required by vertebrates, who synthesize these substances in the skin when under ultraviolet radiation, Animals requiring exogenous sources include infant vertebrates and deficient adult vertebrates, Included there are vitamin D (calciferol ergocalciferol) and vitamin D< (activated 7-dehydrocholesterol cholecalciferol). 

Vitamin D analogs Calcifediol (Calderol) Calcitriol (Rocaltrol) Dihydrotachysterol (DHT, Hytakerol) Ergocalciferol (Calciferol, Drisdol) Generally enhance bone formation by increasing the absorption and retention of calcium and phosphate in the body useful in treating disorders caused by vitamin D deficiency, including hypocalcemia, hypophosphatemia, rickets, and osteomalacia... 

B. The infrared absorption spectmm of a potassium bromide dispersion of the sample, in the range of 2 to 12 pm, exhibits maxima only at the same wavelengths as those of a similar preparation of USP Ergocalciferol Reference Standard. 

C. The ultraviolet absorption spectmm of the sample in alcohol solution exhibits inflections at the same wavelengths as that of USP Ergocalciferol Reference Standard, similarly measured, and the respective absorptivities at 265 nm do not differ by more than 3.0%. 

Early studies showed that, after the administration of [ H]cholecalciferol or ergocalciferol to vitamin D-deficient animals, there is marked accumulation of [ H] calcitriol in the nuclei of intestinal mucosal cells. Physiological doses of vitamin D cause an increase in the intestinal absorption of calcium in deficient animals the response is faster after the administration of calcidiol and faster stUl after calcitriol. There are two separate responses of intestinal mucosal cells to calcitriol a rapid increase in calcium uptake that is due to recruitment of calcium transporters to the cell surface (Section 3.3.2) and a later response from the induction of a calcium binding protein, calbindin-D. 

Cholecalciferol (or Ergocalciferol) is absorbed from the intestinal tract and requires the presence of bile salts, after absorption it is transported to the hver bound to a specific vitamin D-binding protein (alpha-2 globulin). 

Calcitriol is the main active metabolite of vitamin D, and synergizes with parathormone in mobilizing bone calcium and Increasing calcium absorption from the intestine. Vitamin D occurs in a number of sterol forms. These include vitamin D3 (cholecaldferol - the form in foods and made in the skin by the action of UV) vitamin Dj (ergocalciferol -also from plants). These forms are 25-hydroxylated in the kidney, and then la-hydroxylated in the kidney (under the control of parathormone), to make the most active form. This is available as calcitriol. Vitamin D facilitates the absorption of calcium and to a lesser extent, phosphorus, from the intestine and promotes deposition into the bones. A deficiency of vitamin D therefore results in bone deficiency disorders, e.g. rickets in children. Therapeutic replacement of vitamin D in cases of severe deficiency requires quantities of the vitamin best provided by one of the synthetic vitamin D analogues (e.g. alfacalcidol and dihydrotachysterol). 

This could include retinol, cholecalciferol/ergocalciferol, a-tocopherol, vitamin K from food, all of which are more readily absorbed when they can be part of a normal mixed micelle process that occurs with lipid digestion and absorption... 

Vitamin D and its metabolites play an important role in the maintenance of extracellular calcium concentrations and in normal skeletal structure and mineralization. Vitamin D is necessary for the optimal absorption of calcium and phosphorus. On a worldwide basis, the most common cause of hypocalcemia is nutritional vitamin D deficiency. In malnourished populations, manifestations include rickets and osteomalacia. Nutritional vitamin D deficiency is uncommon in Western societies because of the fortification of miUc with ergocalciferol. " The most common cause of vitamin D deficiency in Western societies is gastrointestinal disease. Gastric surgery, chronic pancreatitis, small-bowel disease, intestinal resection, and bypass surgery are associated with decreased concentrations of vitamin D and its metabolites. Vitamin D replacement therapy may need to be administered by the intravenous route if poor oral bioavailability is noted. Decreased production of 1,25-dihydroxyvitamin D3 may occur as a result of a hereditary defect resulting in vitamin D-dependent rickets. It also can occur secondary to chronic renal insufficiency if there is insufficient production of the 1 -a -hydroxylase enzyme for the... 

As would be expected, ds,trans isomerization was accompanied by a shift in absorption maximum to a longer wavelength, from 265 to 270 mp, with a concomitant rise in molecular extinction coefiBcient (see Table II). Ingeniously Dechene (1964) developed a spectrophotometric determination of vitamin D based upon this isomerization reaction. Solutions of ergocalciferol and cholecalciferol in hexane were allowed to react widi iodine of various concentrations under the influence of fluorescent light. He obtained an optimum ratio of iodine to vitamin... 

---