Linkage of autosomal dominant radial drusen (malattia leventinese) to chromosome 2p16-21.

OBJECTIVE: To identify the chromosomal location of the gene involved in the pathogenesis of autosomal dominant radial drusen (malattia leventinese). PATIENTS: Eighty-six members of four families affected with radial drusen; one family of American origin and three families of Swiss origin. METHODS: Family members were clinically examined for the presence of radial drusen. Affected patients and potentially informative spouses were genotyped with short tandem repeat polymorphisms distributed across the autosomal genome. The clinical and genotypic data were subjected to linkage analysis. RESULTS: Fifty-six patients were found to be clinically affected. Significant linkage was observed between the disease phenotype and markers known to lie on the short arm of chromosome 2. The maximum two-point lod score (Zmax) observed for all four families combined was 10.5 and was obtained with marker D2S378. Multipoint analysis yielded a Zmax of 12, centered on marker D2S378. The lod-1 confidence interval was 8 cM, while the disease interval defined by observed recombinants was 14 cM. CONCLUSIONS: The gene responsible for autosomal dominant radial drusen has been mapped to the short arm of chromosome 2. This is an important step toward actually isolating the disease-causing gene. In addition, this information can be used to evaluate other familial drusen phenotypes such as Doyne's macular dystrophy for a possible allelic relationship.

Evidence that stimulatory dopamine receptors may be involved in the regulation of prolactin secretion.

It is well established that dopamine (DA) effectively inhibits PRL secretion from anterior pituitary mammotropes via D2-DA receptors. Paradoxically, it is reported that the monoamine can actually increase PRL release under appropriate experimental conditions. Although the mechanism underlying this stimulatory effect remains undefined, the ability of D1- and D5-DA receptors to activate adenylyl cyclase raises the possibility that a similar receptor subtype is present in the anterior pituitary and mediates the stimulatory effects of DA on PRL release. The purpose of the present study was to explore this possibility. First, we tested whether D1 and D5 receptors could couple to and stimulate PRL secretion. Subclones of GH4C1 cells (which secrete PRL, but do not express DA receptors) stably expressing human D1 or D5 receptors were treated with DA (10(-16)-10(-6) M), and the medium PRL content was measured by RIA. Subclones transfected with short or long forms of the human D2 receptor were also tested. As expected, DA (10(-6) M) inhibited PRL release from cells expressing either short or long D2 receptors by 41% and 39%, respectively (P < 0.01; n = 4 separate experiments). In contrast, comparable concentrations of DA (10(-(8) and 10(-6) M) increased PRL release from cells expressing D1 or D5 receptors by 76% and 122%, respectively (P < 0.01; n = 4). Thus, both D1 and D5 receptors were fully capable of stimulating PRL release from transfected GH4C1 cells. We next sought to determine whether the gene for at least one of these structurally similar receptors was expressed in rat anterior pituitary tissue. First strand cDNA was synthesized, using a rat D5-specific oligonucleotide primer and reverse transcriptase, from total RNA extracted from the anterior pituitary glands of five lactating female rats. The specifically primed cDNA then served as a template for 35 cycles of polymerase chain reaction amplification in which nested primers specific for the rat D5 receptor were used. Electrophoresis of the DNA resolved a 696-basepair band corresponding to a fragment of the D5 receptor in each of five anterior pituitary samples (verified by digestion with three different restriction endonucleases). Taken together, these results demonstrate that both D1 and D5 receptors are capable of mediating the stimulatory effects of DA on PRL release and that the mRNA for DA D5 receptors is present in rat anterior pituitary glands. Our findings support the view that PRL release in vivo may be modulated via one or more stimulatory DA receptors.

Stimulation of lactotrope differentiation in vitro by fibroblast growth factor.

We have reported previously that differentiation of PRL-secreting cells in rats is regulated by a maternal peptide transferred to the neonatal circulation after ingestion of mothers' milk. Inasmuch as milk contains numerous hormones and biologically active peptides, the present study was designed to test the capacity of various growth factors and hypothalamic peptides at inducing the differentiation of PRL cells in vitro. Anterior pituitary cells from 1-day-old rat pups were cultured in a serum-free system for 6 days with a wide concentration range of each test peptide. After this culture period, lactotrope differentiation was assessed by subjecting the anterior pituitary cells to reverse hemolytic plaque assays for PRL. Our efforts were focused on those growth factors and hypophysiotropic peptides found in milk and/or known to regulate pituitary function. Included among these were TRH, GH-releasing factor, somatostatin, vasoactive intestinal peptide, angiotensin-II, insulin-like growth factor-I and -II, LH-releasing hormone, arginine vasopressin, and acidic and basic fibroblast growth factors (aFGF and bFGF, respectively). Of these peptides, only aFGF and bFGF were capable of stimulating lactotrope differentiation. Specifically, we found that maximally effective concentrations of aFGF and bFGF increased the percentage of PRL-releasing cells by almost 8-fold, from about 0.5% to over 4% of all pituitary cells. In addition, bFGF was found to be about 10-fold more potent than aFGF at inducing the differentiation of PRL secretors, with minimum effective doses approaching 10(-11) and 10(-10) M for bFGF and aFGF, respectively. These results suggest that bFGF is a strong candidate to subserve a role in regulating the differentiation of lactotropes in vivo.

Lactotrope differentiation in rats is modulated by a milk-borne signal transferred to the neonatal circulation.

We have previously reported that normal differentiation of PRL-secreting cells in neonatal rats requires a maternal signal specific to the first few days of lactation. Subsequently, we found that milk proteins from this period had a greater capacity than those from later in lactation to stimulate lactotrope differentiation in vitro, suggesting that the maternal signal was a milk-borne peptide. We reasoned in the present study that if this were the case, the signal should be present in the serum of suckling pups, and its level should reflect that in mothers' milk. To test this hypothesis, we first compared serum from 3-day-old pups with that from newborn pups that had not yet suckled. Anterior pituitary cells from 1-day-old pups were cultured for 6 days in the presence of various serum samples (0.01-1.0% by volume). Lactotrope differentiation was assessed using a reverse hemolytic plaque assay for PRL. Serum from 3-day-old pups was more effective (P < 0.01; n = 4) than that from unsuckled newborns at stimulating lactotrope differentiation in vitro (to 3.5 +/- 0.5% and 1.5 +/- 0.5% of all anterior pituitary cells, respectively). Next, we tested whether this increase in serum bioactivity in 3-day-old pups required maternal influences restricted to the first few days of lactation. Newborn pups were placed with foster mothers that had been lactating for 0 or 7 days. When the pups were 3 days old, their serum was tested for lactotrope-differentiating activity. Serum from pups placed with day 0 foster mothers (control) increased the abundance of PRL cells to 2.4 +/- 0.3% of all cells (P < 0.01; n = 3), whereas serum from pups placed with day 7 foster mothers failed to stimulate lactotrope differentiation. In similar experiments, litters placed the day after birth with day 7 foster mothers were separated on day 3 postpartum for 3 h, after which littermates were allowed to suckle for 90 min on different foster mothers on day 3 or 9 of lactation. This brief suckling bout increased (P < 0.01; n = 3) the capacity of serum from pups on day 3 mothers to stimulate PRL cell differentiation (to 3.9 +/- 0.4%) above that of serum from littermates placed with day 9 foster mothers (to 1.8 +/- 0.2%). Finally, the differentiating activities in pup serum and mothers' milk eluted from gel filtration chromatography in identical fractions (4-8 kilodaltons).(ABSTRACT TRUNCATED AT 400 WORDS)

Evidence for bidirectional interconversion of mammotropes and somatotropes: rapid reversion of acidophilic cell types to pregestational proportions after weaning.

The progression from nonpregnancy through late lactation is associated with an increase in the proportion of anterior pituitary cells that secrete PRL and a comparable decrease in the percentage of cells that release GH. These fluctuations result from variations in both the number of cells that release GH or PRL alone and mammosomatotropes, cells that release both hormones concurrently. However, it has not been determined whether this reciprocal shift in PRL and GH secretors during the onset of lactation is readily reversible. In the present study, anterior pituitaries from adult virgin, late lactating, or postweaning female rats (4, 6, or 8 days) were dispersed with trypsin and subsequently assayed for PRL and GH release using reverse hemolytic plaque assays. We found that separating lactating females from their pups for only 4 days induced a reciprocal shift in the proportions of GH and PRL cells back to levels found in virgin females. Simultaneous plaque assays were then performed to determine whether this post-weaning shift in the percentages of GH and PRL secretors was due to changes in the abundance of cells that secrete each hormone alone or in the proportion of mammosomatotropes. The overall changes in GH and PRL cell proportions consisted of variations only in the fraction of cells that secreted either GH or PRL alone; no differences were observed in the percentage of mammosomatotropes or in the overall abundance of acidophils. Our results demonstrate that the reciprocal shifts in the proportions of PRL- and GH-secreting cells associated with lactation are rapidly reversible. Moreover, these results are consistent with our hypothesis that PRL and GH secretors are functionally interconvertible and further suggest that this process is bidirectional.

Is the mammosomatotrope a transitional cell for the functional interconversion of growth hormone- and prolactin-secreting cells? Suggestive evidence from virgin, gestating, and lactating rats.

Serum concentrations of PRL and GH increase and decrease, respectively, during the progression from nonpregnancy through lactation. However, it is unknown whether the secretory capacities and/or relative abundance of cells that release PRL or GH are altered during these physiological states. In the present study anterior pituitaries from adult virgin, gestating, and early or late lactating female rats were dispersed with trypsin and subsequently assayed for PRL and GH release using reverse hemolytic plaque assays. We found that the relative abundance of PRL-secreting cells was greater and that of GH cells lower in pituitaries from lactating females than in those from virgins. Moreover, the relative amounts of both PRL and GH released per cell were diminished in gestating and lactating females. For PRL, this decrease could be accounted for by an increase in the number of cells that released small quantities of hormone. We then performed simultaneous plaque assays to determine whether the shifts in the relative proportions of PRL and GH secretors were due to changes in the percentages of cells that secrete each hormone alone or in the fraction that releases both PRL and GH concurrently. Variations in both single and dual hormone-secreting cells appear to contribute to the overall fluctuations in the relative abundance of PRL and GH cells during these physiological transitions. We conclude that the additional PRL secretors present during lactation may arise from cells that previously released only GH, and that this functional interconversion of GH and PRL secretors might involve an intermediate cell type, the mammosomatotrope.