No abstract

[3H]adenine was taken up by a crude hypothalamic synaptosomal fraction and incorporated into mainly nucleotides. The synaptosomes were superfused and after the initial washout a steady fractional release rate of 0.5-1% of the content/min was found. Electrical pulses (2 ms, 50 Hz, 10-20 mA, 4 min) and veratridine (10 microM, 4 min) induced a Ca++-dependent increase in purine release rate. K+ (30 mM, 4 min) caused a largely Ca++-independent increase. Most of the released material co-chromatographed with adenosine, inosine and hypoxanthine, while little or no nucleotide material was detected. Release of endogenous adenosine, inosine and hypoxanthine was detected by high performance liquid chromatography. However, following hypo-osmotic shock most of the released material was in nucleotides. The removal of glucose from the medium increased the fractional release rate 2-3 fold. Histamine, acetylcholine and glutamate were without effect. High amounts of noradrenaline caused an EGTA-inhibited release of purines, which was un-affected by propranolol or phentolamine. It is suggested that purines are released from neuronal structures and that the release reflects increased energy consumption and/or decreased energy production.

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Theophylline antagonizes several different actions of morphine, including analgesia in mice (Ho ef al. 1973), the inhibitory effect of morphine on electrically induced contractions in the guinea-pig longitudinal muscle myenteric plexus (Sawynok and Jhamandas 1976), the direct stimulatory effect of morphine (Grubb and Burks 1975), and the inhibitory effect of morphine on acetylcholine from brain slices (Jhamandas et al. 1978). The mechanism of action of theophylline is not known. However, theophylline is known to antagonize several actions of adenosine. For example, the inhibitory effect of adenosine on field stimulated guinea-pig longlitudinal muscle is inhibited by theophylline (Sawynok and Jhamandas 1976).Adenosine inhibits acetylcholine and noradrenaline release Jhamandas 1976, Vizi andKnoll 1976, and this effect is also antagonized by theophylline.Theophylline thus inhibits effects of both morphine and adenosine, but the two types of agents are not acting on the same receptors, since adenosine effects are not antagonized by naloxone which readily inhibits morphine effects (Sawynok and Jhamandas 1976, Gustafsson, Hedqvist and Fredholm, unpublished data). The data are, however, compatible with the opinion that morphine induces release of adenosine (or a related compound) and that this accounts at least partly for the effects of morphine. Circumstantial support for such a scheme is provided by the report that the inhibitory effect of morphine on contractions of the field stimulated guinea-pig ileum is potentiated by dipyridamol (Gintzler and Musacchio 1975), a compound known to potentiate the effects of adenosine by inhibiting its inactivation.We report the preliminary finding that morphine enhances depolarization induced release of adenosine and other purines from rat cortical slices.After decapitation the rat brains were rapidly dissected out. Thin slices (0.5-1 mm) of the occipital cortex were cut by a razor blade. From the middle of the slice a circular section (7 mm diam) was punched out. 4 slices were incubated at 37°C in 5 ml Krebs-Ringer bicarbonate buffer for 40 min with 10 ,uCi 2,8-3Hadenine, 14C-adenine or I-7-3H-noradrenaline (Radiochemical Centre, Amersham). On the average some 10 nCi was taken up per slice. After washing, the slices were placed in thermostated plastic chambers and superfused with Krebs-Ringer bicarbonate buffer of the following composition (mM): NaCl (1 18), KCI (4.89, CaCI, (0.25), + MgSo, (l.15), KH,PO, (1.15), NaHCO, (25) glucose ( l l . l ) , pH 7.2-7.4 gassed with 95% 0, and 5 % CO,.Samples of the superfusion solution were continuously taken and the radioactivity counted in a scintillation coctail consisting of 4 g/l Omnifluor (Packard) in toluene Triton X-100 (2: 1). At the end of the ex- 502

It has been suggested that the deficient lipolytic response to catecholamines in hypothyroidism may be due to an increased sensitivity to adenosine and/or increased adenosine levels in this condition. We confirmed that the addition of adenosine deaminase enhanced the lipolytic response of hypothyroid fat cells, but the stimulation was at least as large in euthyroid cells. Adenosine analogs were more potent as antagonists of NA-induced lipolysis in hypothyroid than in euthyroid fat cells, but the difference could be explained by a decreased response to NA. Suspensions of hypothyroid cells accumulated more purine nucleosides (115 +/- 20) than did euthyroid cells (48 +/- 8 pmol/30 min/10(5) cells; p less than 0.01). This difference could not be explained by a lower rate of adenosine elimination, which occurred by three different pathways: uptake followed by phosphorylation, uptake followed by deamination and deamination by the serum albumin preparation. Under certain circumstances the latter pathway is of overwhelming importance. Fat cells from mature rats (460-480 g) behaved similarly as cells from young control rats. Thus, the changes induced by hypothyroidism was not due to a developmental change. The results are discussed in relation to earlier findings on the alterations in catecholamine responsiveness in hypothyroidism. It is concluded that an increased influence of adenosine could possibly explain some aspects of altered catecholamine responsiveness. If it does the mechanism is likely to involve an enhanced amount of adenosine rather than an increased sensitivity to adenosine.