The chromosomes of 14 species of amphisbaenians (Amphisbaenia, Reptilia)

The chromosomes of 14 species belonging to eight amphisbaenian genera are here reported. The karyotypes of nine species all comprise 6 pairs of metacentric macrochromosomes (M) and 7 to 12 pairs of microchromosomes (m). The M in these species are similar to one another in morphology. One species, <i>Geocalamus acutus, </i>has 7 pairs of M and 12 pairs of m; two of the M are telocentric, perhaps as a result of centric fission of one pair of metacentric M. The remaining four species, <i>Bipes biporus, Amphisbaena alba, A</i>. <i>fuliginosa, </i>and <i>A</i>. <i>innocens, </i>had higher diploid numbers and wide variations in morphology. <i>B</i>. <i>biporus </i>had 10 pairs of biarmed M and 11 pairs of m. <i>A</i>. <i>alba </i>had 11 pairs of M, 7 biarmed and 4 telocentric, and 8 pairs of m. <i>A</i>. <i>fuliginosa </i>had 11 pairs of M, only 3 biarmed and 8 telocentric, and 13 pairs of m. <i>A</i>. <i>innocens </i>also had 11 pairs of M, 4 biarmed and 7 telocentric, and 14 pairs of m. The karyotypes of these four species are so different from one another and from those of the remainder of the group that it was not possible to assess their cytogenetic relationships. A distinct and independent sequence of chromosomal evolution was presumably involved in each case. No heteromorphic pair or monosomy was observed in either male or female amphisbaenians.

Mechanism of triglyceridemia in hypercholesterolemic rabbits

To elucidate mechanisms responsible for the increased plasma triglyceride (TG) which occurs in diet-induced hypercholesterolemia in rabbits, albino rabbits were fed a 3% cholesterol diet for various durations, and the following determinations were carried out: plasma lipid levels; turnover rate of plasma TG (labeled very low density lipoprotein, or glycerol-2- 3 H method); lipoprotein lipase activity of the heart and plasma; fatty acid and acetate incorporation into TG in the liver (homogenates and slices). Plasma levels of both free and esterified cholesterol and phospholipid increased rapidly, while TG increased relatively slowly during cholesterol feeding without change in hepatic TG synthesis. The fractional turnover was, on the other hand, depressed within a week. The decrease in plasma TG in response to a heparin injection was less in hypercholesterolemic rabbits than in normal animals. However, the measured activity of heart lipoprotein lipase of cholesterol-fed rabbits was higher than that of the control group. When the effects of two substrates (very low density lipoprotein from normo- and from hypercholesterolemic plasma) were compared, the apparent activity was lower with the latter. The Degrees of this inhibition was proportional to the amount of cholesterol in the lipoproteins. The inhibition of lipoprotein lipase activity was also observed with the addition of cholesterol to activated Ediol, but not with addition of esterified cholesterol. Lineweaver-Burk plots were constructed using partially purified plasma lipoprotein lipase, and Km values for Ediol, Ediol plus protamine sulphate, and Ediol plus cholesterol were calculated. The presence of cholesterol in the substrate of lipoprotein lipase competitively inhibits the enzyme activity, and this is the mechanism of hyperglyceridemia observed in diet-induced hypercholesterolemic rabbits.