Progestin receptors in brain and pituitary of 20-day-old fetal mice: an autoradiographic study using [125I]progestin

The distribution of progestin target sites in the brain and pituitary of estrogen-primed 20-day-old fetal mice was investigated by thaw-mount autoradiography. Three pregnant mice were each implanted sc with a Silastic tube containing estrogen on day 17 and ovariectomized on day 19 of gestation. Twenty-four hours after ovariectomy 10 fetuses (5 males and 5 females) were collected and each injected sc with 0.33 microgram/100 g BW [125I]progestin (SA, 2200 Ci/mM). For competition, two additional fetuses were injected with 20 micrograms R5020 1 h before (Z)-17 beta-hydroxy-17 alpha-(2[125I]iodovinyl)4-estren-3-one [( 125I]Progestin) to demonstrate that nuclear uptake and retention of radioactivity were specific for progestin. Two hours after injection of [125I]Progestin all fetuses were mounted, frozen, and sectioned in a cryostat. After 1-37 days of exposure, sections were developed and scanned for labeled cells. Cells with nuclear concentration were found in the male and female preoptic area, within certain nuclear groups in the basal hypothalamus, in the central gray of the midbrain, and in the pituitary. No labeling was detected in the cortex or amygdala. The results indicate that cells in certain regions of the brain and pituitary express progestin receptors at the end of gestation and suggest that progesterone is important for the normal development of these cells.

The rat androgen receptor: primary structure, autoregulation of its messenger ribonucleic acid, and immunocytochemical localization of the receptor protein

A composite androgen receptor DNA sequence 4,181 base pairs in length was determined from three cDNA clones isolated from a rat epididymal bacteriophage lambda gt11 library. An open reading frame of 902 amino acids encodes a protein of 98,227 mol wt. Structural domains characteristic of the steroid receptor family include an amino-terminal region with five repeated amino acid motifs, a central DNA-binding domain homologous with other steroid receptors, and a carboxyl-terminal steroid-binding region. A receptor cDNA probe used in Northern blot analysis hybridized with a predominant 10-kilobase androgen receptor mRNA in male reproductive tissues of the rat. Autoregulation of androgen receptor mRNA was indicated in rat ventral prostate by an increase in the level of 10-kilobase mRNA after castration and suppression of receptor mRNA upon androgen restimulation. A 15 amino acid peptide with sequence derived from the deduced androgen receptor sequence was synthesized and used as immunogen in raising receptor antibodies in rabbits. Antisera reacted with high titer against the synthetic peptide by enzyme-linked immunosorbent assay and against the native [3H]dihydrotestosterone-labeled androgen receptor as evidenced by an increase in receptor sedimentation rate determined by sucrose gradient centrifugation. Immunocytochemical staining localized the androgen receptor to epithelial cell nuclei in rat ventral prostate.

The human androgen receptor: complementary deoxyribonucleic acid cloning, sequence analysis and gene expression in prostate

Androgenic hormones mediate their effects on male sex differentiation and development through a high affinity receptor protein. We report here cloning of the complete coding sequence of the human androgen receptor (hAR). By sequence homology hAR is a member of the nuclear receptor family, with closest sequence identity to the progesterone, mineralocorticoid, and glucocorticoid receptors. Regions of highest homology include the DNA-binding domain and a small region within the hydrophobic ligand-binding domain. Comparison of the deduced 919 amino acid sequence of hAR (98,999 mol wt) to the 902 amino acid sequence of rat AR (98,227 mol wt) reveals identical sequences in the DNA- and hormone-binding domains, with an overall homology of 85%. In human prostate, the major androgen receptor mRNA species is 10 kilobases while a less abundant mRNA is approximately 7 kilobases. Rabbit polyclonal antibodies were raised against a synthetic peptide from the N-terminal region of hAR. Immunocytochemical analysis of human prostate tissue demonstrated that AR is localized predominantly in nuclei of glandular epithelial cells.

The distribution of progesterone receptor in the 20-day-old fetal mouse: an autoradiographic study with [125I]progestin

The distribution of progestin target sites in 20-day-old fetuses of estrogen-primed pregnant mice was investigated by thaw-mount autoradiography. Pregnant mice received a Silastic estradiol implant on day 17 and were ovariectomized on day 19 of pregnancy. Twenty-four hours after ovariectomy 10 prematurely delivered fetuses were each injected with 0.33 microgram/100 g BW [125I]progestin (SA, 2200 Ci/mM). To show specificity of progestin localization two additional fetuses were each injected sc with 20 micrograms R5020, a synthetic progestin, 1 h before the injection of [125I]progestin. The fetuses were frozen 2 h after injection of [125I]progestin, sectioned, and processed for thaw-mount autoradiography. Cells with nuclear uptake and retention of radioactivity were observed in numerous tissues, including certain regions of the oral mucosa and developing teeth, esophagus, larynx, skin, mammary gland, skeletal muscle, kidney, and reproductive glands and ducts. Injection of unlabeled R5020 1 h before [125I]progestin prevented nuclear concentration of radioactivity in all target tissues. The results indicate that progesterone receptors are expressed with a regional, cellular, and subcellular distribution in term fetal mouse tissues and suggest that progesterone is important to the growth and development of certain fetal tissues.

Distribution of progestin-concentrating cells in rat brain: colocalization of [3H]ORG.2058, a synthetic progestin, and antibodies to tyrosine hydroxylase in hypothalamus by combined autoradiography and immunocytochemistry

The anatomical distribution of progestin-concentrating cells in rat brain was investigated by thaw-mount autoradiography. Fifteen 23-day-old ovariectomized and adrenalectomized female Holtzman rats were injected sc with 5 micrograms 17 beta-estradiol in oil/100 g BW daily for 4 days. On the fifth day, all animals were injected iv with 1 microgram/100 g BW [3H]ORG.2058, a synthetic progestin. The animals were killed after 30 or 60 min, and the brains were frozen and processed for autoradiography. Nuclear concentration of radioactivity was found in certain cells of the forebrain and midbrain and was prevented by prior injection (15 min) of excess unlabeled ORG.2058. In the preoptic-septal region, progestin-labeled neurons were observed in the nucleus (n.) septi lateralis, n. interstitialis striae terminalis, n. preopticus medialis, n. preopticus lateralis, n. preopticus periventricularis, and n. preopticus suprachiasmaticus. In the hypothalamus, labeled neurons were seen in n. periventricularis hypothalami, n. arcuatus hypothalami, n. ventromedialis hypothalami, n. dorsomedialis hypothalami, n. premammillaris ventralis, n. premammillaris dorsalis, and lateral hypothalamus. In the extrahypothalamic region, a few labeled cells were found in the central, medial, and cortical nuclei of the amygdala, the organum subforniculare, the lateral geniculate nucleus, the parietal and entorhinal cortex, and the central gray of the midbrain. Some of the progestin-concentrating cells were characterized with combined autoradiography and immunocytochemistry. Tyrosine hydroxylase-containing cells of the arcuate nucleus and the hypothalamic periventricular nucleus (group A12) showed nuclear concentration of radioactivity. Tyrosine hydroxylase cells in groups A11, A13, and A14; the substantia nigra (group A9); and the ventral tegmental area (group A10) did not show nuclear concentration of [3H]ORG.2058. The autoradiographic study demonstrates specific progestin-binding sites in nuclei of neurons in select areas of the rat brain. The results of combined autoradiography and immunocytochemistry suggest, for the first time, a direct action of progestin on tuberoinfundibular dopaminergic neurons.

Sites of action of gossypol studied by autoradiography and enzyme histochemistry

The distribution of 14C-gossypol acetate was studied by autoradiography in male rats after intraperitoneal or intratesticular injection. Accumulation of radioactivity was found in testis, kidney and liver, while there was little in brain, pituitary and epididymis. In testis, high accumulation occurred in interstitial cells, with low levels in Sertoli cells, spermatogonia and spermatocytes. In addition, the chronic effect of gossypol was assessed by enzyme histochemistry with thiamine pyrophosphate, alpha-glycerophosphate dehydrogenase, and by lipid stain. In the treated animals an increased number of luminal exfoliated cells (Sertoli cells, germ cells and spermatids) was noted, which showed positive reactions. The results suggest both direct and indirect effects of gossypol on testicular functions.

Pyloric gastrin-producing cells and pyloric sphincter muscle cells are nuclear targets for 3H 1,25(OH)2 vitamin D3. Studied by autoradiography and immunohistochemistry

Autoradiographic studies were conducted to identify and characterize target cells for 1,25(OH)2 vitamin D3 in the pyloric region of rats and mice. After injection of 3H 1,25(OH)2 vitamin D3, nuclear concentration of radioactivity was observed in nuclei of duodenal epithelium and certain cells of pyloric glands, while most of the epithelial cells in the pyloric and gastric glands did not show nuclear labeling. In combined immunohistochemical studies, cells in the pyloric glands that showed nuclear concentration of radioactivity, were stained in their cytoplasm with antibodies to gastrin. Also, cells of the pyloric sphincter muscle showed nuclear labeling, in contrast to cells of the duodenal muscularis, which remained unlabeled under the conditions of the experiments. The results indicate that the cells with nuclear radioactivity contain receptors for 1,25(OH)2 vitamin D3 and suggest that gastrin secretion and pyloric muscle functions are regulated by a direct action of 1,25(OH)2 vitamin D3 on these cells.

1,25-Dihydroxyvitamin D3 target cells in immature pancreatic islets

Target cells of 1,25-dihydroxyvitamin D3 were identified by autoradiography in islets from rats of different ages. Nuclei of pancreatic islet cells selectively concentrated 1,25-[3H]dihydroxyvitamin D3 but not 25-[3H]hydroxyvitamin D3 or 24,25-[3H]dihydroxyvitamin D3. Developmental studies of pancreatic islets indicated that target cells, as revealed by significant nuclear concentration of 1,25-[3H]dihydroxyvitamin D3, are present in islet cells of fetal rats. The percentage of islet cells that concentrated 1,25-[3H]dihydroxyvitamin D3 increased from 10 to 15% in the fetus to 60% at 1 day of age. Immunocytochemical staining indicated that insulin-containing cells but not glucagon or somatostatin cells concentrated 1,25-[3H]dihydroxyvitamin D3. Peak uptake of 1,25-[3H]dihydroxyvitamin D3 was calculated to be 400 pmol/mg DNA, with no significant difference in nuclear accumulation between islet cells from neonatal and adult rats or between islets in vivo and isolated islets in vitro. The results of these studies indicate that 1,25-[3H]dihydroxyvitamin D3 target cells are present in islets before pancreatic beta-cells are morphologically or functionally mature; islet beta-cells concentrate 1,25-dihydroxyvitamin D3, but not 25-hydroxyvitamin D3 or 24,25-dihydroxyvitamin D3. We conclude that only the 1,25-dihydroxyvitamin D3 metabolite of vitamin D is accumulated by nuclei of developing and mature beta-cells and suggest that 1,25-dihydroxyvitamin D3 plays a role in the maturation of islet beta-cells.

Immunocytochemical localization of the gonadotropin-releasing hormone-associated peptide of the LHRH precursor

Using specific rabbit anti-GAP (gonadotropin-releasing hormone-associated peptide) serum, we have immunocytochemically localized GAP in the rat brain. Immunostaining of neuronal perikarya, fibers and terminals was demonstrated with GAP antiserum under conditions of tissue preparation which make immunostaining with LHRH antisera difficult or undetectable. GAP-immunoreactive perikarya were observed in sections of perfused or nonperfused brains without colchicine pretreatment. Using a double immunoperoxidase staining method, both GAP and LHRH immunoreactivities were shown to coexist in the same neurons. The common distribution of LHRH and GAP immunoreactivity in the rat brain is strongly supportive of GAP representing the non-LHRH portion of the LHRH precursor. The use of GAP antisera that can distinguish between LHRH and the remaining portion of its prohormone represents a valuable tool for studies of LHRH-prohormone processing and distribution.

Are estrogen receptors cytoplasmic or nuclear? Some immunocytochemical and biochemical studies

The subcellular localization of estradiol receptor (ER) has been examined using various experimental approaches. Immunocytochemical studies using the monoclonal antibody JS 34/32, raised against calf uterine cytosolic ER, yielded only equivocal results. In general, cells and tissues pretreated with estradiol showed positive immunostaining in the nuclei whereas those not exposed to the steroid did not show any staining. Nuclear translocation of ER was examined in intact MCF-7 cells using compounds which are known to influence receptor activation. When MCF-7 cells were exposed to molybdate (20 mM), nuclear translocation was completely inhibited while dithiothreitol (20 mM), dibutyryl cAMP (1 microM) and dibutyryl cGMP (1 microM) increased the translocation 2-3-fold. Phenol red, at the range of concentrations generally used in tissue culture media, also increased translocation. The physiological validity of such translocation was examined using cellular progesterone receptor (PR) synthesis as a specific parameter. When MCF-7 cells were grown in media containing phenol red for 48 h, the PR synthesis increased significantly. We further examined whether cytoskeletal proteins are involved in the translocation of ER. Colchicine, an inhibitor of microtubule assembly, inhibited translocation of ER in MCF-7 cells at 1-10 microM. PR synthesis was also inhibited by colchicine in a dose-dependent manner. It may be concluded from these and other published data that ER may not be located at all times in a single subcellular compartment but may rather exist in a dynamic equilibrium between the plasma membrane, cytoplasm and nucleus.

Vitamin D sites of action in the pituitary studied by combined autoradiography-immunohistochemistry

Adult male and female mice under normal diet were injected with 3H 1,25(OH)2 vitamin D3 and sacrificed 3.5 h afterwards. Autoradiograms were prepared according to our thaw-mount technique and stained with antibodies to pituitary hormones. Thyrotropes showed strong and extensive nuclear concentration of radioactivity: about 90% of the immunostained thyrotropes were labeled. Lactotropes, somatotropes and gonadotropes showed no or only weak nuclear radioactivity: a subpopulation of 5%-10% of each of these immunostained cell types displayed nuclear labeling that was weak when compared to thyrotropes. Neural lobe pituicytes also showed weak to intermediate nuclear labeling. The results indicate a presence of nuclear receptors for 1,25(OH)2 vitamin D3 in pituitary cell types and suggest direct but differential genomic effects of 1,25(OH)2 vitamin D3 on pituitary hormone secretion. Evidence further suggests the existence of a vitamin D regulated brain-pituitary-thyroid axis.

Immunohistochemical localization of estrogen receptor in rat brain, pituitary and uterus with monoclonal antibodies

Localization of estrogen receptor (ER) in rat brain, pituitary and uterus is shown by the avidin-biotin complex technique using a monoclonal antibody, JS34/32. Immunostaining is observed in nuclei of certain neurons in the preoptic-septal region, hypothalamus and amygdala, and in cells of the anterior pituitary and uterus after estradiol stimulation. Staining is specific since preadsorbed JS34/32 antibody with purified cytoplasmic ER as well as a control monoclonal antibody do not show positive immunoreaction. In the brain, neither cytoplasmic nor nuclear staining is seen in the absence of estradiol stimulation, nor with the progesterone and dihydrotestosterone treatments. The distribution of ER-containing neurons in specific areas of the brain overlaps with the distribution of estrogen target neurons demonstrated by autoradiography. The results demonstrate the usefulness of the monoclonal antibody for the detection of ER in target tissues.

Autoradiographic studies with 3H dihydrotestosterone in the brain of sex reversed mice, heterozygous for androgen insensitive testicular feminization (Tfm). A comparison with normal female mice and sex reversed male mice

Specific binding sites for 3H dihydrotestosterone are demonstrated by autoradiography in brain nuclei of sex reversed mice heterozygous for testicular feminization (Tfm) which are phenotypically intersexes with testes and accessory sex glands that consist of a mosaic of androgen insensitive Tfm cells which lack specific dihydrotestosterone binding and androgen sensitive normal cells. The nuclear group evaluated include: nucleus (n.) septi lateralis, n. interstitialis striae terminalis, n. medialis amygdalae, the hypothalamic n. arcuatus, n. ventromedialis lateralis, n. pre-mammillaris ventralis, n. preopticus medialis, and nuclei of the cranial nerves VII, X, and XII. In the sex reversed males and the female, used as controls, the frequency of neurons with specific DHT binding show a distinct male-female difference in the caudal part of the arcuate nucleus. In the sex reversed Tfm heterozygotes, in all brain nuclei studied, the frequency of labeled neurons is reduced. The extent of reduction of androgen binding in the different brain nuclei varies among as well as within individual sex reversed Tfm heterozygotes, suggesting variations of the ratio of normal to Tfm neurons in sex reversed Tfm heterozygotes. The differentially reduced androgen binding of different brain systems corresponds to a differentially reduced androgen dependent behaviour reported in the literature.

Autoradiographic determination of catechol estrogen binding sites in brain, pituitary and uterus

The anatomical pattern of nuclear binding of 2-OH[6,9-3H]estradiol ([3H]2-OHE2) in brain, pituitary and uterus have been studied autoradiographically. Autoradiograms of forebrain, pituitary and uterus show nuclear concentrations of radioactivity in certain cells. This nuclear concentration is abolished when unlabelled 2-OHE2 or E2 was injected prior to the injection of [3H]2-OHE2. In the brain nuclear labelling is observed in the septal-preoptic region, in the anterior hypothalamic area, and in the central hypothalamic area. Some estrogen-sensitive nuclear groups, such as lateral septum and hippocampus, do not show accumulation of radioactivity. In the uterus, luminal and glandular epithelium, stromal cells and muscle cells are labelled. A comparison of the quantitative nuclear uptake of radioactivity and of the different time intervals after the injection of different doses shows similar uptake of nuclear radioactivity. This is comparable to data obtained after [6,7-3H]estradiol ([3H]E2) injection. The results provide clear evidence for nuclear binding of catechol estrogens of the same magnitude as [3H]E2 after in vivo treatment.

Differential distribution of 3H dihydrotestosterone and 3H estradiol nuclear binding sites in mouse male accessory sex organs. An autoradiographic study

The distribution of specific nuclear binding sites for androgens and estrogens in the male accessory sex organs of the mouse was assessed by autoradiography with 3H dihydrotestosterone (3H DHT) and 3H estradiol (3H E2). With 3H DHT nuclear labeling differed among the epithelia of the organs. It was high in seminal vesicle and ampullary gland, moderate in ventral prostate, urethral gland, prostatic excretory ducts and the ampulla ductus deferentis, low in dorsal prostate and low or absent in coagulation gland. With 3H E2, in contrast, epithelial nuclear labeling was high only in coagulation gland, moderate or low in seminal vesicle, low or absent in ventral and dorsal prostate and absent in ampullary gland and ampulla ductus deferentis. In the lamina propria of all organs nuclear labeling with 3H DHT was generally moderate and existed only in some cells, with the highest number in the ampulla ductus deferentis. With 3H E2, nuclear labeling in the lamina propria showed a high intensity in all organs, except in ventral and dorsal prostate which remained unlabeled. Many labeled cells were found in the deferent duct and its ampulla, while in the other organs only a few cells showed nuclear labeling with 3H E2. In the smooth muscle sheath of all organs, some muscle cells were moderately labeled with 3H DHT, but not with 3H E2. The results indicate the presence of nuclear receptors in male accessory sex organs for both dihydrotestosterone and estradiol. The differential patterns of 3H DHT and 3H E2 nuclear uptake suggest differential sensitivities of the individual organs and their tissue compartments for androgens and estrogens.

Topographical and developmental studies on target sites of 1,25 (OH)2 vitamin D3 in skin

Tritium-labeled 1,25 (OH)2 vitamin D3, when injected into vitamin D-deficient adult and pregnant rats is concentrated and retained strongest in nuclei of cells in the outer root sheath of the hair, followed by the stratum granulosum, spinosum, and basale of the epidermis. In the hair follicle, in addition to the most heavily labeled outer root sheath, nuclear labeling exists also in cells of the hair bulb and of the inner root sheath, as well as in basal cells of the sebaceous gland. In contrast, cells of the dermal papilla and the connective tissue of the dermis are generally unlabeled, except for labeled cells in the outer connective tissue sheath at the infundibulum of vibrissae of 20-day fetal rats and a few scattered labeled cells in the dermis, probably macrophages. In the developing hair, in 18- and 20-day fetal rats, a distinct topographic pattern of labeled cells can be seen, which is characteristic of the different stages of hair follicle development. In the hair germ, heavily labeled cells appear first in the stratum spinosum. In the hair peg, they remain in this position in its juxtaepidermal portion; however, when a dermal papilla develops, heavily labeled cells assume a marginal position. This suggests a sequential epidermal-epidermal and mesenchymal-epidermal receptor induction. Injection of tritium labeled 25 (OH) vitamin D3 did not show nuclear concentration in these tissues and excess unlabeled 25 (OH) vitamin D3--unlike excess 1,25 (OH)2 vitamin D3--did not prevent nuclear uptake of tritium labeled 1,25 (OH)2 vitamin D3. The results indicate differential effects of 1,25 (OH)2 vitamin D3 on different structures in the epidermis and dermis.

Estradiol is concentrated in tyrosine hydroxylase-containing neurons of the hypothalamus

Localization of [3H]estradiol in tyrosine hydroxylase-containing neurons of rat brain was shown by a combined technique of autoradiography and immunohistochemistry. [3H]Estradiol was concentrated in the nuclei of tyrosine hydroxylase-containing neurons in the nucleus arcuatus, nucleus periventricularis hypothalami, and the zona incerta. These results suggest that estradiol acts directly on dopamine-producing neurons of the tuberoinfundibular system and incertohypothalamic system.

Localization of aldosterone and corticosterone in the central nervous system, assessed by quantitative autoradiography

Nuclear localization of tritiated aldosterone in the CNS was studied in rats by numerical evaluation of silver grains, deposited over neuronal cell nuclei in thaw-mounted autoradiograms, and compared with the localization obtained after prior administration of a 100-fold excess of radioinert aldosterone, corticosterone or 18-hydroxy-11-deoxycorticosterone (18-OH-DOC). Corticosterone and 18-OH-DOC completely prevented nuclear localization in most regions examined. However, in contrast to pretreatment with aldosterone, pretreatment with corticosterone and 18-OH-DOC did not completely prevent the concentration of radioactivity in the cell nuclei of the indusium griseum. Traces of radioactivity were, furthermore, retained in areas CA1 and CA2 and the dentate gyrus in rats exposed to corticosterone, but not to 18-OH-DOC, prior to [3H]aldosterone. A similar profile of silver grain distribution to that noted with aldosterone was found for corticosterone except that with tritiated corticosterone the most intense concentration of radioactivity occurred in hippocampal areas CA1 and CA2 and not in the indusium griseum. Prior administration of excess deoxycorticosterone acetate abolished nuclear accumulation of tritiated corticosterone. Dihydrotestosterone, on the other hand, failed to compete with tritiated corticosterone at a dose 200-fold in excess of the tritiated steroid. We conclude that (1) a receptor readily shared by aldosterone, corticosterone, 18-OH-DOC and DOC, but not by dihydrotestosterone, is widely distributed throughout the CNS, (2) a receptor shared by aldosterone and 18-OH-DOC, but not by corticosterone may be present in hippocampal areas CA1 and CA2, (3) that both these as well as the receptor accepting dihydrotestosterone can be located within the same cell.

Differential distribution of dihydrotestosterone and estradiol binding sites in the epididymis of the mouse. An autoradiographic study

The distribution of androgen and estrogen binding sites in the mouse epididymis was assessed by autoradiography with 3H dihydrotestosterone (3H DHT) and 3H estradiol (3H E2). Nuclear labeling with 3H DHT in principal cells of the epithelium is high in the caput, low in the corpus, and high again in the cauda. 3H E2 also binds to the nuclei of principal cells. The pattern is distinct from 3H DHT: nuclear labeling is highest in the ductulus efferens and high in the caput, but low or absent in corpus and cauda. Apical cells in caput and clear cells in corpus and cauda are moderately labeled with 3H DHT but heavily labeled with 3H E2. Connective tissue cells show variable labeling with both hormones, being more pronounced with 3H E2. Smooth muscle cells are also labeled to varying degrees with both hormones. The different binding patterns of 3H DHT and 3H E2 and the results of the competition studies with unlabeled compounds demonstrate that in the epididymis besides the specific nuclear receptors for androgen also estrogen receptors are present.

Topographic distribution of progestin target cells in hamster brain and pituitary after injection of [3H]R5020

The topographic distribution of progestin concentrating cells in the female hamster brain and pituitary was studied by thaw-mount autoradiography. Fifteen minutes after injection of [3H]R5020, a synthetic progestin, nuclear uptake and concentration of radioactivity was found in certain cells of the forebrain and midbrain, as well as in the anterior pituitary. Competition studies with unlabeled R5020 abolished and with progesterone reduced the nuclear uptake of radioactivity. In the forebrain, radioactively labeled cells are observed in n. septi lateralis, n. interstitialis striae terminalis, n. preopticus medialis and lateralis, n. periventricularis hypothalami, organum subfornicale, n. arcuatus hypothalami, n. ventromedialis hypothalami, n. dorsomedialis hypothalami and n. premammillaris ventralis. In the midbrain a few labeled cells are found in the griseum centrale. In the anterior pituitary, labeled cells are identified by immunostaining as luteinizing hormone-producing cells. The results of the autoradiographic study demonstrate nuclear progestin binding sites and suggest genomic action of progestin on the labeled structures, probably related to the modulation of gonadotropin secretion and sexual behavior in the brain and pituitary.

Autoradiographic localization of target cells for 1 alpha, 25-dihydroxyvitamin D3 in bones from fetal rats

Thaw-mount autoradiographic studies after injection of 3H-1,25-D3 were conducted on 18- and 20-day-old rat fetuses. In maxillary bones, ribs, and tibia, nuclear concentration of radioactivity was found in osteoprogenitor cells and osteoblasts. Osteocytes and chondrocytes in epiphyseal plates were either unlabeled or weakly labeled. In competition experiments, nuclear concentration of radioactivity was blocked by the injection of a high dose of nonradioactive 1,25-D3 prior to the administration of the labeled hormone, but not by a similar dose of nonradioactive 25-D3. The results are interpreted as indicating that osteoprogenitor cells and osteoblasts are target cells for the direct action of 1,25-D3 on fetal bone.

Target cells for 1,25-dihydroxyvitamin D3 in developing rat incisor teeth

The concentration of radioactivity is observed in the nuclei of pulpal cells of maxillary and mandibular incisors of 20-day-old fetal rats, following injection of [3H]-1,25 (OH)2 vitamin D3. Cells in the odontoblast and ameloblast layers are essentially free of nuclear labeling. The radioactively labeled pulpal cells exist throughout the length of the incisors with the exception of the progenitor areas. The results indicate the presence of receptors for 1,25 (OH)2 vitamin D3 in pulpal cells, and suggest the effects of the hormone on these cells.

Autoradiographic localization of 1,25-dihydroxyvitamin D3 in rat placenta and yolk sac

After injection of 3H-1,25-(OH)-vitamin D3 into rats on days 18 and 20 of pregnancy, autoradiograms of placenta and fetal membranes show nuclear concentration of radioactivity in certain cells. This nuclear concentration is abolished when unlabeled 1,25-(OH)2-vitamin D3, but not 25-(OH)-vitamin D3, is injected prior to the labeled hormone. Nuclear labeling is observed in epithelial cells of visceral yolk sac and amnion, and in certain trophoblasts in basalis and labyrinth. The results suggest the presence of a specific receptor-like binding for 1,25-(OH)2-vitamin D3 and thus involvement of the target cells in calcium regulatory mechanisms during development.