Joyce J. Repa

Protein selection by rats adapted to high or moderately low levels of dietary protein

After preliminary studies on flavor acceptability, patterns and indices of subsequent feeding behavior were monitored by computer in young rats which were adapted to 15% or 70% casein diets before being offered, sequentially, choices between flavored diet pairs in which the proportions of percentage casein were 5/65, 5/55, 5/45, 5/35 and 5/25. Similarly adapted rats received these choices in the reverse sequence. Rats adapted to 15% casein usually ate randomly from the diet pairs and selected approximately 15-30% casein; individual behaviors were prominent. The 70% casein groups avoided the higher casein diet, often within minutes (except for the first-offered 5/25 choice), and seldom selected more than 10% casein; individual differences were infrequent. Such rats also distinguished between flavored 70% and 65% casein diets. Sizes and numbers of meals and rates of eating differed for the paired diets, especially for rats adapted to 70% casein. A flavor added to the 70% casein adaptation diet was not avoided when present only in the 5% casein diet of a 5/65 choice. Rats adapted to 70% soy protein before receiving flavored 5/65 to 5/25 choices selected 20-28% soy protein, a level far above those of casein selections by rats adapted to 70% casein. Dietary adaptation and type of protein thus affect subsequent diet selection and feeding patterns and indices.

All-trans 3,4-didehydroretinoic acid equals all-trans retinoic acid in support of chick neuronal development.

All‐trans 3,4‐didehydroretinoic acid (at‐ddRA) has been identified as a biologically important retinoid in avian, but not mammalian, embryonic development. In this report, we show that at‐ddRA, like all‐trans retinoic acid (atRA), supports the survival and differentiation of sympathetic neurons of the embryonic chick. Furthermore, the expression of the retinoid‐responsive gene RARβ2 is increased in neurons exposed to either at‐ddRA or atRA. The mechanism whereby at‐ddRA exerts its effects in chick neurons may involve binding to and activation of nuclear retinoid receptors. For this reason, the binding of recombinant chick RARβ2 to at‐ddRA and to receptor‐specific DNA response elements was examined and compared with the binding characteristics of recombinant murine RARβ2. The chick RARβ2, like the mammalian RAR, binds to [3H]atRA with high affinity (Kd=0.7‐2 nM). Furthermore, both chick and murine RARβ2 bind equally well to at‐ddRA, atRA, and 9‐cis RA, but neither receptor shows appreciable binding to 13‐cis RA. The chick RARβ2 recognizes previously described retinoic acid response elements of mammalian gene promoters and, like mammalian RARβ2, shows enhanced binding in the presence of RXR. This study provides evidence that at‐ddRA, like atRA, supports neuronal development in the chick by its interaction with nuclear retinoid receptors.—Repa, J. J., Plum, L. A., Tadikonda, P. K., Clagett‐Dame, M. All‐trans 3,4‐didehydroretinoic acid equals all‐trans retinoic acid in support of chick neuronal development. FÁSEBJ. 10,1078‐1084 (1996)

N-linked analogs of retinoid O-glucuronides: potential cancer chemopreventive/chemotherapeutic agents

Glucuronide metabolites of retinoic acid (RA) and its analogs have been suggested to be active cancer chemopreventive/chemotherapeutic metabolites of the parent molecule. The glucuronide of RA is relatively unstable, thus we prepared N-linked glycoside analogs of RA that are nonsubstrates for β-glucuronidase in efforts to improve efficacy. The synthesis and biological activity of the analogs are reported.

Norleucine : a branched-chain amino acid analog affecting feeding behavior of rats

Norleucine, an isomer of leucine and isoleucine and a potent competitor of large neutral amino acid transport into brain, thereby depleting certain amino acid pools, was tested for its effects on growth and feeding behavior of rats fed an amino acid diet limiting in leucine. Growth and food intake were depressed in proportion to the dietary level of norleucine (0.2 to 1.1% of the diet). With suboptimal amounts of indispensable amino acids, leucine at 150% of the requirement reversed the effects of 0.2 and 0.5% norleucine; slight excesses of the other indispensable amino acids were required with extra leucine for maximum growth with 1.1% norleucine. Rats almost exclusively preferred the control to the norleucine diet, but not if the latter diet also contained leucine. Rats also strongly selected a nonprotein rather than norleucine diet when this was the first available choice. If the first choice was between the nonprotein and control diets, rats later almost exclusively selected the norleucine-containing rather than the nonprotein diet for varying periods (2 to 6 days). These studies suggest that amino acid analogs may be useful agents in the study of animal behavior associated with changes in brain amino acid pools.

Avoidance of GABA-containing diets by olfactory bulbectomized rats

In order to test the importance of olfaction in the avoidance of GABA-containing diets by intact rats, olfactory bulbectomized and sham-operated control rats were allowed to choose between a low protein control diet and this diet supplemented with 2.5% GABA; the specificity of the response was examined by also testing for responses to other amino acids. Both groups of rats markedly avoided the GABA diet initially; the bulbectomized rats later tended to increase their intake of this diet. The bulbectomized rats chose similar amounts from the control diet and one supplemented with alanine whereas the control rats ultimately strongly preferred the latter diet. Both groups only moderately avoided a threonine-supplemented diet. The results suggest that (1) the odor of GABA is not critical in the avoidance of diets containing this amino acid; and (2) patterns of food selection from diets containing GABA differ from choices from diets containing other small neutral amino acids such as alanine or threonine.

Synthesis and receptor binding affinity of conformationally restricted retinoic acid analogues

Abstract In an effort to synthesize two conformationally restricted retinoids utilizing a cyclopropyl ring as bioisostere for the C9–C10 double bond, we describe the synthetic strategies and retinoid receptor binding affinity of the trans -cyclopropyl analogue and the unexpected epimerization of the cis -cyclopropyl analogue.

Dietary GABA and Food Selection by Rats

Abstract To obtain further information pertaining to amino acid-induced alterations in feeding behavior, studies were performed to examine the food choices made by rats fed low protein diets made more or less aversive by the addition of various amino acids. When rats were allowed to choose between two diets, they preferred a low protein control, threonine-imbalanced or nonprotein diet to one containing 2.5% γ-aminobutyric acid (GABA). Acceptance increased when GABA content was lowered to 1.5%; rats preferred this diet when the alternative diet was made sufficiently aversive. There were large individual differences among rats selecting from pairs of unacceptable diets. Avoidance of, or preference for, a given diet is clearly affected by the relative aversive qualities of the offered pair of diets.

Choices by rats between water and solutions of GABA or other amino acids

Responses differed widely when rats were offered choices between water and solutions of GABA, its isomers alpha-aminobutyric acid (AABA) and alpha-aminoisobutyric acid (AIB), or of another 4-carbon amino acid, threonine. They preferred solutions of threonine and AABA starting at concentrations of about 30 mM; preference for threonine declined when its concentration was 330 mM or above. Rats never preferred GABA or AIB, but instead avoided these amino acids when concentrations were approximately 100 mM or above. Control rats showed strong preferences for drinking from a given location. Limited studies with humans showed variations in the concentrations at which they could detect GABA; the mean was about 0.06 mM, a concentration far below that at which rats began to avoid this amino acid. The ability of dietary GABA to depress food intake of rats (as shown in earlier studies) does not seem related to a uniquely high sensitivity to its gustatory qualities.

Alleviation in the rat of a GABA-induced reduction in food intake and growth

Cold exposure and diet dilution which stimulate food intake of normal rats lessened depressions of food intake and growth induced by dietary GABA. During a 3-day adaptation to the cold, rats fed a diet containing 4.5% GABA lost weight; thereafter, food intake and growth rate differed little from those of cold control rats and were usually greater than those of normal rats fed GABA. Hepatic GABA-aminotransferase activity of cold-exposed rats fed the GABA diet increased to about twice that of normal control rats. Rats fed a control diet diluted by half with cellulose ate 50% more of this diet than of the undiluted diet but gained only 20% less weight. Rats ate twice as much of a diluted, 9% GABA diet as of an undiluted, 4.5% GABA diet (thus doubling their GABA intake) and gained three times as much weight. A novel food (condensed milk) barely lessened the adverse responses to GABA. These results show that conditions requiring rats to increase their food intake in order to maintain body weight can also increase their acceptance of a diet high in GABA.

Acceptability by rats of aqueous solutions of amino acid analogues

Preferences differed widely when rats were offered choices between water and solutions of various natural amino acids and structurally related analogues. They avoided the branched-chain amino acid valine but preferred solutions of its isomer norvaline and of norleucine. The hydrochloride forms of ornithine and arginine were preferred to water at concentrations up to about 100 mM and avoided at 410 mM; homoarginine.HCl was never preferred and was avoided at 39 and 78 mM. Rats were indifferent to taurine and beta-alanine at most concentrations but refused these amino acids at high concentrations (205 and 410 mM, respectively). In conjunction with earlier observations on feeding behavior in response to dietary additions of amino acids, the results show that selections by rats between water and amino acid solutions cannot be used to predict choices among amino acid-containing diets.