Homogenates of rat hypothalamic tissue were fractionated by means of discontinuous sucrose density gradient centrifugation. Immunoreactive luteinizing hormone releasing hormone (LHRH), thyrotropin releasing hormone (TRH), and α-melanocyte stimulating hormone (α-MSH) were found to be concentrated in the synaptosome-enriched fraction. This fraction was suspended in 0.32 M sucrose and the release of the three peptides was investigated. After incubation, the synaptosomes were re-isolated by ultrafiltration, and the concentration of each peptide in the ultrafiltrate was determined by radioimmunoassay. When the synaptosomal fraction was incubated at 30° C in 0.32 M sucrose containing either 60 mM K+-2 mM Ca2+ or 140 mM Na+ alone a release of LHRH, TRH, and α-MSH occurred. Of the total content 30-50% of LHRH but only about 10% of TRH and α-MSH was releasable. When the synaptosome preparation was preincubated for 30 min at 30°C with 10-4 M vinblastine. K+- as well as Na+-induced release of LHRH, THR, and α-MSH was inhibited, and the stimulatory effect of each cation was almost totally blocked by preincubation with 5×10-4 and 10-3 M vinblastine. The inhibitory action of vinblastine (5×10-4 M) did not affect the oxidation of glucose to CO2 by the synaptosomes. The results of the present investigation demonstrate that synaptosome-enriched fractions of hypothalamic origin are more stable with respect to LHRH, TRH, and α-MSH release during incubation in isotonic sucrose than they are in ionic solutions, and that the peptides are released by a vinblastine-sensitive mechanism.
|Original language||English (US)|
|Number of pages||6|
|Journal||Pflügers Archiv European Journal of Physiology|
|State||Published - May 1 1980|
ASJC Scopus subject areas
- Clinical Biochemistry
- Physiology (medical)