Cholecalciferol 25-hydroxylation is similar in liver microsomes from male and female rats when cholecalciferol concentration is low.

We compared cholecalciferol 25-hydroxylation in liver microsomes of male and female rats. The rate of production of 25-hydroxycholecalciferol was similar in liver microsomes from female rats and those from male rats when cholecalciferol concentration ranged from 50 to 200 nmol/L. The liver cytosolic fraction stimulated the 25-hydroxylase activity of the microsomes up to 100% in both male and female rats at 44 nmol/L cholecalciferol. Cytosol metabolized cholecalciferol to a currently unidentified metabolite. At 300 nmol/L cholecalciferol, synthesis of the cytosolic metabolite was 100% greater than at 100 nmol/L and coincided with 32% lower synthesis of 25-hydroxycholecalciferol. These results suggest similar 25-hydroxy-lase activity in liver microsomes from male and female rats and similar ability of liver cytosol from these rats to stimulate 25-hydroxylation at low nanomolar concentrations of cholecalciferol, whereas inhibitory effects of cytosol at higher concentrations of cholecalciferol were shown.

Changes in synaptic integration during the growth of the lateral giant neuron of crayfish.

1. The effect of growth on the electrotonic structure and synaptic integrative properties of the lateral giant (LG) interneuron was assessed from anatomic and electrophysiological measurements of LGs in small (1-2.4 cm) and large (9-11.2 cm) crayfish and from calculated responses of mathematical models of these neurons. Postsynaptic responses of small and large LGs were compared with model responses to determine whether the differences in the neurons' responses result from growth-related changes in their physical characteristics. 2. LG neurons in the terminal abdominal ganglia of small and large crayfish are similar in shape but differ in size according to an approximately isometric pattern of growth. The soma diameter of the large LG is 2.2 times larger than the small LG, the major ipsilateral dendrite is 2.8 times longer and 3.6 times greater in diameter, and the axon is 7.6 times longer and 4.5 times greater in diameter. The projected area of the major ipsilateral dendrite of LG in the horizontal plane of the terminal abdominal ganglion is 27 times larger in the large than in the small crayfish. 3. LG's input resistance was nearly 80% smaller in the large (167 K omega) than in the small (742 K omega) crayfish when measured at or near the initial axon segment. The cell's membrane time constant displayed an opposite relationship, with the value in the large crayfish (20.9 ms) nearly two-and-a-half times larger than the value in the small crayfish (8.6 ms). 4. Simultaneous recordings were made from the distal portion of the ipsilateral dendrite and the initial axon segment of small and large LGs to determine how excitatory postsynaptic potentials (EPSPs) are attenuated or filtered by the electrotonic properties of the different sized cells. In the small LG, the fast alpha and the slower beta components of compound EPSPs evoked by sensory nerve stimulation were similarly attenuated. In the large LG, the alpha component of the compound EPSP was much more attenuated and smoothed than the slower beta component. 5. Multicompartment models of small and large LGs were constructed and used to test whether differences in the two neurons' physical properties could account for the differences in their passive response properties.(ABSTRACT TRUNCATED AT 250 WORDS)