L F Tseng

Thyrotropin releasing hormone antagonizes β endorphin hypothermia and catalepsy

Abstract Injection of 30 μg β endorphin intraventricularly (ivt) in rats produced an alteration of body temperature, a state of catalepsy, and an increase in antinociceptive latencies. Subsequent ivt injections of 20 μg of thyrotropin releasing hormone (TRH) reversed the ongoing changes in body temperature and catalepsy produced by β endorphin. Since TRH antagonized these effects in hypophysectomized rats, it is implied that these effects of TRH are independent of pituitary-thyroid involvement. In contrast to the above, TRH did not alter the antinociception produced by β endorphin in either sham-control or hypophysectomized rats. The failure of TRH to antagonize all three of these opiate effects, as well as the inability of TRH to displace bound dihydromorphine from synaptic plasma membranes, suggests that the level of TRH-β endorphin interaction is not at the opiate receptor.

Comparison of the behavioral effects of β-endorphin and enkephalin analogs

Abstract The behavioral effects of β-endorphin, enkephalin analogs, morphine and etorphine were briefly compared. In the tail-flick test in mice and in the wet shake test in rats, β-endorphin and D-Ala 2 -D-Leu 5 -enkephalin had equal antinociceptive activity; D-Ala 2 -Met-enkephalinamide and D-Leu 5 -enkephalin were less active. The order of activity of the enkephalin analogs and opiate alkaloids for stimulating locomotor activity in mice paralleled their analgesic activities; β-endorphin, however, had only minimal stimulatory actions. Morphine sulfate, 50 μg injected into the periaqueductal gray, produced hyperactivity but this effect was not observed with etorphine or opioid peptides. By contrast, “wet dog” shakes was observed with the opioid peptides but not with either opiate alkaloid. These heterogenous behavioral responses, which were all antagonized by naloxone, indicate that multiple types of receptors mediate the effects of opiates in the central nervous system.

β-Endorphin: Complete primary structure is required for full analgesic activity

Abstract The synthesis of βh-endorphin-(1–30) has been accomplished by the solid-phase procedure and its analgesic potency was assayed by the tail-flick method. Results showed that the synthetic analog had only 56% activity of the parent molecule. Thus, the complete sequence of 31 amino acid residues in βh-EP is required for full analgesic activity.

[D-Thr2, Thz5]- and [D-Met2 ,Thz5]-enkephalinamides: potent analgesics by intravenous injection.

Abstract Two enkephalin analogs, [D-Met 2 , Thz 5 ]-enkephalinamide and [D-Thr 2 , Thz 5 ]-enkephalinamide, have been synthesized by the solid-phase method. When injected centrally, [D-Thr 2 , Thz 5 ]-enkephalinamide is 3.5 times more potent than the [D-Met 2 , Thz 5 ] analog. However, the two are equipotent and 4.2–4.8 times more potent than morphine when injected intravenously.

Opioid properties of β-lipotropin fragment 60-65, HArgTryGlyGlyPheMetOH

The pharmacologic activity of the hexapeptide fragment corresponding to the amino acid fragment 60–65 in β-lipotropin, (β-LPH-(60–65)) was studied in vitro and in vivo. In binding assays on synaptosomal plasma membrane the peptide was found to be equipotent to met-enkephalin, but behaved differently to cations; in contrast to met-enkephalin both Mn+2 and Na+ enhanced the binding of β-LPH-(60–65) to synaptosomal plasma membrane. On both the quinea pig ileum and mouse vas deferens β-LPH-(60–65) inhibited contractions elicited by electrical stimulation and each effect was reversible by naloxone. On the guinea pig ileum β-LPH-(60–65) was equipotent to met-enkephalin and 0.5 as potent as normorphine but on the vas deferens it was 4.6 times more potent than normorphine. The activities of β-LPH-(60–65) appear to be due to the intact compound rather than to its conversion to met-enkephalin, since the peptide extracted from the ileum assay was found to behave identically as β-LPH-(60–65) with high pressure liquid chromatography. When β-LPH-(60–65) was administered centrally to mice and rats, no overt central actions were observed and an antinociceptive effect could not be demonstrated. Nor did β-LPH-(60–65) antagonize morphine action or precipitate the withdrawal syndrome in morphine dependent animals. It is concluded that the good agreement which generally exists between in vitro and in vivo assay procedures for opiate-like activity of morphine and its surrogates does not necessarily hold for the endogenous peptides with similar actions.

β-Endorphin: Deletion of a single amino acid residue abolishes immunoreactivity but retains opiate potency

Abstract Two synthetic analogs of camel β-endorphin, one with omission of Leu-14 and the other with omission of Asn-20, have been assayed for immunoreactivity by radioimmunoassay, opiate activity in the guinea pig ileum preparation and analgesic potency in mice. It was found that the omission analogs had no immunoreactivity, but retained significant biological activities. As far as we are aware, this is the first instance in which deletion of a single amino acid residue in a biologically active peptide abolished immunoreactivity.