The localization of a plasma membrane calcium pump in the oviduct of the laying hen was investigated by immunohistochemical techniques, utilizing a monoclonal antibody (5F10) produced against the human erythrocyte calcium pump. This antibody was shown to react with an epitope of the pump in oviductal tissue, and prominent staining was observed on the microvilli of the tubular gland cells of the hen shell gland (uterus) and the isthmus. The Ca2+ pump was not detectable in the infundibulum or the magnum. Calbindin-D28k, also localized by immunohistochemical means, was observed to be present in the tubular gland cells of the shell gland and the distal isthmus (adjacent to shell gland) but not in either the proximal isthmus (adjacent to the magnum), the magnum or the infundibulum. The localization of the Ca2+ pump in the oviduct corresponds to known sites of mineral deposition during egg shell formation. The distribution of calbindin-D28k differed, co-localizing with the Ca2+ pump in the shell gland and distal isthmus but not in the proximal isthmus. This might reflect a greater rate of active Ca2+ secretion in the distal isthmus and shell gland as compared to the proximal isthmus.

Determination of the Effect of 1,25(OH)2D3 on Calcium Absorption. Series 1. These experiments were designed to determine the temporal relationship between the stimulation of calcium absorption by 1,25(OH)2D3 and the appearance of CaBP. In one experiment, the chicks were injected intracardially with 1 Ag of 1,25(0H)2D3 in propylene glycol at time 0, and the degree ofduodenal absorption of 47Ca and the presence of CaBP in the mucosal tissue were determined 1, 2, 4, or 8 hr later. The absorption period was 30 min. In the second experiment, the protocol was the same except that the chicks received 300 ng of 1,25(0H)2D3 and the absorption period was 15 min.Series 2. Vitamin D3 [2 international units (IU) per day for 6 days] was administered orally to rachitic chicks before further treatment. In the first experiment, the partially repleted chicks were injected intracardially with 1,25(OH)2D3 or vehicle (propylene glycol) and the same protocol as for the rachitic chicks (see Series 1) was followed. In the second experiment, the rachitic chicks were divided into two groups: one group was partially repleted with vitamin D3 (2 IU/day) for 6 days and the other group received vehicle only. The chicks were further divided into two subgroups and injected intracardially with 300 ng of 1,25(0H)2D3 in propylene glycol or with vehicle, and the absorption of 47Ca and the appearance of CaBP were determined 1 or 2 hr later.Calcium Absorption Procedure. Calcium absorption was determined by the in situ ligated-loop procedure, with 47Ca as tracer, as described (17). The absorption period was 15 or 30 min. Residual 47Ca in the excised loop was measured with a Beckman Gamma-300 gamma counter with the discriminator set to exclude contributions from the 47Sc daughter. Absorption was calculated as 100 minus the percentage of 47Ca remaining in the segment. After measurement of radioactivity, the same segment was further analyzed for its CaBP content.As part of the last experiment of series 2, the net accumulation of 47Ca by the intestinal tissue was determined by re- 7939The publication costs ofthis article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U. S. C. §1734 solely to indicate this fact.

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