Streptozotocin toxicity to cultured pancreatic islets of the Syrian hamster

Pancreatic islets of the Syrian golden hamster were maintained in culture for extended periods of time. Toxicity of streptozotocin in these cultures was evaluated by measurement of insulin secretion. Exposure of islets to 1 or 2 mM streptozotocin immediately following isolation resulted in a permanent and dose-related inhibition of insulin secretion. This was accompanied by islet disruption as observed by phase-contrast microscopy. Culture of islets for 24 hours before streptozotocin exposure afforded protection from toxicity. For example, exposure of freshly isolated islets to 2 mM streptozotocin resulted in complete destruction of beta cells, whereas islets similarly exposed after a 24 hr culture period continued to secrete insulin for many months. Islets maintained in culture for one week before exposure to 0.1–0.5 mM streptozotocin, however, became more sensitive than freshly isolated islets. Repeated weekly exposure of cultured islets to a non-toxic concentration (0.1 mM) resulted in sustained suppression of insulin secretion after 11 weeks.     

Cobalt blocks the decrease in MEPSP frequency on depolarization in calcium-free hypertonic media

Media made hyperosmotic with sucrose increase the frequency of spontaneously released quanta of transmitter, or miniature excitatory postsynaptic potentials (MEPSPs). In calcium-free medium, depolarization with high potassium reduces the MEPSP frequency, presumably due to calcium efflux in the reversed gradient condition. This effect of depolarization is blocked by cobalt, supporting the above interpretation of the effects of hypertonicity and depolarization and suggesting that cobalt can block efflux as well as influx through calcium channels.     

Synergistic effects of 1,25(OH)2D3 and 24,25(OH)2D3 on duodenal CaBP in rachitic chicks and on eggshell weight in Japanese quails

The role of 24,25(OH)2D3 in calcium homeostasis is still controversial. In the present study the administration of low doses of 1,25(OH)2D3 and of higher doses of 24,25(OH)2D3 either alone or in conjunction with each other, were studied in rachitic chicks and in Japanese quails. Whereas 24,25(OH)2D3 alone had no significant effect on duodenal CaBP and on alkaline phosphatase in chick serum, it increased the influence of 1,25(OH)2D3 on these two parameters strongly. Also, when 1,25(OH)2D3 and 24,25(OH)2D3 were given simultaneously to Japanese quails, calcium excretion via the egg shell was clearly higher than when either metabolite had been administered alone. These results indicate that 1,25(OH)2D3 and 24,25(OH)2D3 exert a strong synergistic effect in rachitic animals.     

Palatability and digestibility of soya- and milk proteins in Callithricidae

4 protein sources were tested for palatability, digestibility, influence on bodyweight and consistency of faeces in Callithrix jacchus and Saguinus fuscicollis. The protein sources were incorporated at crude protein levels of 12, 17 and 22% in a pelleted diet. A banana supplement was also fed which reduced the total protein content to 10.7, 14.7 and 18.3%. The test diets, fed for 3 weeks, were well accepted with the milk proteins being slightly preferred. Consumption of the 12% protein pellets was greater than their 22% equivalents. True protein digestibility was calculated to be 97% for lactalbumin, 96% for casein, 90% for soy protein concentrate and 83% for soyabean meal. Changes in bodyweight were negligible. Dry matter of faeces varied between 25% (lactalbumin diets) and 28% (casein diets), but did not change with increasing protein intake. Increasing levels of cellulose, from 2.4 to 7.2% total crude fibre lowered the apparent protein digestibility from 84.3 to 79.2% and the digestibility of dry matter from 82.2 to 76.5%.     

The nucleotide sequence of a nematode vitellogenin gene.

The nematode, Caenorhabditis elegans, contains a family of six genes that code for vitellogenins. Here we report the complete nucleotide sequence of one of these genes, vit-5. The gene specifies a mRNA of 4869 nucleotides, including untranslated regions of 9 bases at the 5' end and 51 bases at the 3' end. Vit-5 contains four short introns totalling 218 bp. The predicted vitellogenin, yp170A, has a molecular weight of 186,430. At its N terminus it is clearly related to the vitellogenins of vertebrates. However, the vit-5-encoded protein does not contain a serine-rich sequence related to the vertebrate vitellin, phosvitin. In fact, the amino acid composition of the nematode protein is very similar to that of the vertebrate protein without phosvitin. Vit-5 has a highly asymmetric codon choice dictionary. The favored codons are different from those favored in other organisms, but are characteristic of highly expressed C. elegans genes. The strong selection against rare codons is not as great near the 5' end of the gene; rare codons are 15 times more frequent within the first 54 bp than in the next 4.8 kb.     

Photoperiod influences the annual reproductive cycle of the male pallid bat (Antrozous pallidus)

Adult pallids bats collected in April or May, were maintained in short or long photoperiods (10 or 14 h light/day) for 3-6 months. In August, the short-day bats had regressed testes, epididymal spermatozoa and fully developed accessory sex glands, corresponding to the autumnal reproductive condition of field animals; long-day bats had testes undergoing spermatogenesis, few epididymal spermatozoa and undeveloped accessory sex glands (summer reproductive condition). Bats in each photoperiod manifested the expected autumnal reproductive pattern in October. We suggest that photoperiod influences the reproductive physiology of male pallid bats by affecting an endogenous circannual reproductive rhythm.     

Circannual and seasonal variations in plasma luteinizing hormone levels of ovariectomized ground squirrels (Spermophilus lateralis)

Plasma luteinizing hormone (LH) levels were determined at monthly intervals in intact and ovariectomized squirrels maintained in a constant 14L:10D photoperiod at a temperature of 23 +/- 2 degrees C. LH was undetectable (less than 0.9 ng/ml) in plasma of intact females at all times of year. Females ovariectomized (OVX) at 9.5 months of age in March showed substantial increases in plasma LH in May and June but LH was undetectable between July and November. Females ovariectomized at 13 months of age in July first manifested detectable LH levels the following January and February (6-7 months post-ovariectomy). Very few adult females trapped in May and ovariectomized in August had detectable LH levels within 2 months of ovariectomy; however, females ovariectomized the following February had detectable LH titers 1 month later. Long-term studies of individual OVX squirrels indicated peak LH levels between March and June, 1980, relatively low or undetectable titers between August and December and elevated LH levels between January and March, 1981. The results are suggestive of a circannual rhythm of LH secretion which appears restricted to one season of the year and occurs independently of steroid feedback from the ovaries; ovarian steroids only modulate the levels of plasma LH during the brief annual period of hypothalamo-hypophysial activity. We suggest that onset and termination of LH release are mediated by central nervous system circannual clocks.     

Improved Solid Medium for the Detection and Enumeration of Pectolytic Bacteria

An improved solid agar medium (MP medium) has been developed which allows detection of pectolytic activity in bacteria. Organisms tested exhibited a variety of regulatory controls governing pectate lyase synthesis. The medium contains mineral salts, pectin, and yeast extract. After growth of the organisms, the agar plate is flooded with a polysaccharide precipitant, and pectolytic activity is shown by clear zones around active colonies. High concentrations of phosphate are shown to be necessary for pectic enzyme formation on solid media. The medium has successfully been used to detect pectolytic organisms in soil, forest litter, and rotting vegetable samples.     

THE INDUCTION OF FLOWERING IN NICOTIANA. II. PHOTOPERIODIC ALTERATION OF THE CHLOROGENIC ACID CONCENTRATION

Chlorogenic acid and its 2 isomers, believed to be the 4– and 5–0-caffeoylquinic acids, have been extracted from leaves of photoperiodic species of Nicotiana, separated by column chromatography (gradient elution) and measured quantitatively during the course of photoperiodic induction. In both N. tabacum cultivar ‘Maryland Mammoth’ (a short-day plant) and N. sylveslris (a long-day plant), the change of the meristem from the vegetative to the flowering shape is preceded by a rise in the chlorogenic acid content of the leaves. During the differentiation of the flower primordia in the shoot apex, there is a drop in the concentration of the chlorogenic acid in the leaves, which is especially marked in the short-day species. The levels of the 2 isomers decrease also at that time. There is no change in the ratios of the 3 caffeoylquinic acids during photoperiodic induction. In both the long- and the short-day species, the 3-isomer (chlorogenic acid) is present at the highest concentration. In the short-day species, there is more of the 4-isomer than of the 5-isomer, whereas in the long-day species, the level of the 5-isomer equals or surpasses that of the 4–0-caffeoylquinic acid.