Differences in resistance to ventricular fibrillation between hibernators and non-hibernators

Abstracts--Strategies m cold Symposmm t e m p e r a t u r e under conditions of c o n s t a n t d a r k n e s s . Body temperature cycles with an amplitw/e of 0.75 - 1.25"C were r e c o r d e d i n hibernation and the onset of p e r i o d i c arousal a c t i v i t y showed the same phase relationship as the prior nonhfbernatory s t a t e . Temperatures recorded in field hlbern a c u l a a v e r a g e d 4.6°C o v e r the h i b e r n a t i o n s e a s o n . Faergence of : ~r~r~'efs from hibernation is cued by increasing soil temperatures. A l l f i e l d and l a b o r a t o r y p o p u l a t i o n s emerged from hibernation when the hlhernsculum temperatur~ was between 8.0 - 9.5°C. This cuing mechanism will only induce arousal in field and laboratory populations during the presumptive spring s e a s o n under a p p r o p r i a t e p h y s i o l o g i c a l conditions.

THE EKG OF SMALL HIBERNATORS ~ D BEARS. G. Edgar Folk, Jr., Richard C. Simmonds and Mary A. F o l k . Department of P h y s i o l ogy and B i o p h y s i c s . The U n i v e r s i t y of Iowa, Iowa C i t y , IA, 52242, USA. The EKG was recorded of 3 species of bears, of arctic marmots, and woodchucks, by implanted radio capsule. We r e p o r t e d e a r l i e r t h a t b l a c k b e a r s , g r i z z l y b e a r s and p o l a r b e a r s have a s l e e p i n g summer h e a r t r a t e of 40 to 50 bpm, but i n w i n t e r dormancy r e d u c e the r a t e t o 8 to i 0 bpm. T h e i r body t e m p e r a t u r e i s reduced only 7 o r 8"C. With newer c a p s u l e s we were a b l e to r e c o r d t h e e l e c t r o c a r d i o g r a m in su~aer and in winter. Such records are a clue to the identification of hibernator s p e c i e s . The c l a s s i c hibernators such as woodchucks and h a m s t e r s a r e known t o have a v e r y s h o r t QT i n t e r v a l , which means t h a t r e p o l a r i z a t i o n of the v e n t r i c l e o c c u r s r a p i d l y a f t e r c o n t r a c t i o n . For comparison, QT i n t e r v a l s of marmots, woodchucks, polar bears, b l a c k b e a r s , g r i z z l y b e a r s and man, a l l a s l e e p and u s i n g th e same t e l e m e t r y equipment, showed ( e x p r e s s e d as mean, i n seconds, with S . E . ) : Marmot 0 . 1 5 ± 0 . 0 3 ; woodchuck 0 . 9 t 0 . 0 1 ; p o l a r b e a r O.11 t 0 . 0 1 : g r i z z l y b e a r 0 . 2 3 ± 0 . 0 6 ; man 0 . 4 5 . Summer s l e e p and w i n t e r h i b e r n a t i o n ( e x c e p t f o r man) were compared: t h e r e was l i t t l e d i f f e r e n c e . In h i b e r n a t i o n : marmot 0 . 1 7 ± 0 . 0 2 ; woodchuck 0 . 1 6 ± 0 . 0 1 : b l a c k bear 0.27 ± 0.06: grizzly bear 0.31 ± 0.06. aecause this study shows t h a t h e a r t s of h e a r s a r e p h y s i o l o g i c a l l y s i m i l a r to t h o s e of o t h e r h i b e r n a t o r s , and be c a use of o t h e r p h y s i o l o g i c a l e v i d e n c e , i t seems J u s t i f i e d t o use t h e d e s i g n a t i o n of " h i b e r n a t o r " f o r p o l a r b e a r s , g r i z z l y b e a r s , and b l a c k bears. Supported by the N a t i o n a l S c i e n c e Founda tion.

DIFFERENCES IN RESISTanCE TO VE~:TRICULAR FIBRILLATIOn! BETWELN IIIBE~NATORS AND NON-HIBERNATORS. Duker, G6ran, J o h a n s s o n , Bengt W.. O l s s o n , S v e n - O U e . AB F e r r o s a n , Fack, S-201 i0 Malm~ I, Sweden: and Heart Section, General Hospital, S-214 Ol Malm~, Sweden. There are d i f f e r e n c e s between hibernators and n o n - h l b e r n a t o r s i n the susceptibility to ventricular fibrillation (VF). In a comparison between g u i n e a p i g s (G) and hedgehogs (H) VF could never be induced i n H be means of: i) local application of sconitlne on the epicardlum 2) administration of 0.55 M CaCll to an isolated heart perfused with a K-free Tyrode solution 3) injection of procaln IICI into isolated hearts perfused with a Tyrode solution after previous adrenaline administration, o r 4) ligation of the LAD coronary artery In an attempt to clarify these differences the hearts of G and H were studied electrophyslologleally. Urethanea n e s t h e t i z e d and artificially resplrated open chest H (0.9 - 1.2 kg, n=7) and albino G (0.35 - 0.55 kg, n-12) were used. By use of bipolar electrodes, attached to the right and left ventrlcular epicardium, the heart was paced and given extra stimuli defined in strength, duration and delay after the p a c i n g stimulus. Following parameters were measured: I) t h r e s h o l d value 2) maximal following frequency 3) effective r e f r a c t o r y period (ERP) 4) fibrillation t h r e s h o l d Compared tO G the H Imd a higher threshold (0.49 ± 0.17 mA and 0.28 ± 0.07 mA) and a lower maximal following frequency (7.6 ± l.g IIz and 12.4 ± 1.7 Ha). All (12/12) G developed v e n t r i c u l a r premature b e a t s (VPB) and VF, whereas o n l y 43% ( 3 / 7 ) of 11 d e v e l o p e d VPB and 50% ( 3 / 6 ) VF. A g r e a t e r stimulus current and lower frequencies were needed to induce VPB and VF in t h e H, when compared to the G, i n d i c a t i n g t h a t the resistance to VF is higher in the H than i n the C. The ERP, however, was not different.

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nique. Each h e a r t was i n i t i a l l y p e r f u s e d a t 25"C f o r 15 min and t h e r e a f t e r t e m p e r a t u r e was d e c r e a s e d ( I ' C / 4 mln) u n t i l ventrlcular arrest occurred. Isotonic contractile tension and s p o n ta n e o u s h e a r t r a t e were r e c o r d e d w l t h a PHP-4 P h y s i o g r a p h c o n n e c t e d to a type B myograpb. C o n t r o l h e a r t s from both s p e c i e s were p e r f u s e d with Krebs R i n g e r B i c a r b o n a t e (KRB) c o n t a i n i n g g l u c o s e (200 mS/100 ml) and e q u l l l b r a t e d w i t h 95% 02 - 5% CO2. To t e s t t h e h y p o t h e s i s t h a t r e t e n t i o n of cardiac f u n c t i o n a t low temperatures may i n v o l v e maintenance of C-~'lP ( c y c l i c adenosine 3 ' 5 ' monophosphate), r a t hearts were perfused w i t h KRB containing t b e o p h y l l i n e (lO - 2 , 10 -3 or 10"~ ~) o r lmidsaole (10-iM) and ground s q u i r r e l hearts Were perfused w i t h lmidazole (10 -2 or 10-3 R). Theophy111ne was chosen to i n h i b i t phosphodiesterase, increase l e v e l s of C-AHP, and p t s s i b l y enhance hypotbermic tolerance in r a t hearts. lmidazole was chosen to s ti m ul ate phosphodiesterase, decrease C-AHP, and p o s s i b l y a l t e r th e a b i l i t y of ground s q u i r r e l h e a r t s to t o l e r a t e low t e m p e r a t u r e s . Ground s q u i r r e l h e a r t s remained f u n c t i o n a l below 4"C whereas rat hearts f a i l e d a t a mean t e m p e r a t u r e of 1 3 . 1 " C. S q u i r r e l h e a r t s m a i n t a i n e d cont r a c t i o n a m p l i t u d e t o 6°C and e x h i b i t e d msxlmum t e n s i o n d e v e l o p ment a t 8.5"C whereas r a t h e a r t s f a i l e d to m a i n t a i n contract i o n amplitude below 14.5"C and e x h i b i t e d maximum tension development at 17.5"C. Theophylllne or lmldazole did not significantly alter the arrest temperature of rat or squirrel h e a r t s but th e d r u g s d e p r e s s e d c o n t r a c t i o n a m p l i t u d e i n h e a r t s from both s p e c i e s . T h e o p h y l l i n e (10 - 2 ~) produced I n complete r e l a x a t i o n i n r a t h e a r t s . The r e s u l t s o b t a i n e d w i t h t h e o p h y l l i n e s u g g e s t mechanisms o f a c t i o n i n v o l v i n g C-AHP r e l a t e d e f f e c t s as w e l l a s d i r e c t e f f e c t s on non-C-AMP c o n t r a c t i l e mechanisms of th e sarcolemma and t h e s a r o o p l s s m i c retIculum. The decrement in c o n t r a c t i l e f o r c e produced by i m i d a z o l e l a p r o b a b l y r e l a t e d to d e c r e a s e d C - ~ which l e a d s to a s u p p r e s s e d Ca4"+ f l u x d u r i n g t h e c o n t r a c t i l e c y c l e . Normal l e v e l s of C-AHP are apparently not necessary f o r the squirrel heart to remain functional below 5°C.

SEASONAL CHANGES IN PLASMA I,~4UNO-REACTIVE INSULIN IN THE GARDEN D O ~ O U S E (ELIGUYC ~UERCINUS) AND IN HIE GROUND SQUIRREL (CITELLUS TRIDEC~I,VEATUS). L. Ambid and R. Agid, EPA 412 CNRS, Institut de Fhysiologie, 31400 Toulouse, France. Plasma g l u c o s e i n th e h l b e r n a t l n g garden dormouse d e creases g r a d u a l l y , a l l the more slowly as the a~bient temper atur e i s low, from 120 ± 7 mg% t o 29 ± 5 mg% and the c e l l s of the pancreas are r e p l e t e w i t h s ec r eti on granules. During arousal the breakdown o f l i v e r glycogen leads to hyperglycemia. These changes In blood g l u c o s e do not o c c u r i n the ground s q u i r r e l . In both s p e c i e s , a r o u s a l b r i n g s about a tremendous i n c r e a s e i n plasma g l y c e r o l , FFA and l a c t a t e . In o r d e r to e x p l a i n t h e s e f l n d l n g s , we s t u d i e d t h e changes In th e plasma i m m u n o - r e a c t l v e i n s u l i n ( I . R . I . ) l e v e l In r e l a t l o n to th e s e a s o n a l c y c l e and t o th e h l b e r n s t l o n c y c l e . H i b e r n a t i o n was induced by p l a c i n g th e a n i m a l s i n th e d a r k room a t 6"C w i t h food a v a l l a b l e ~ ~ b i S u m . In th e dormouse plasma I . R . I . l e v e l r i s e s from 16 ~U/ml In autumn and w i n t e r to 26 ~U/ml in May, then decreases i n June t o 13 uU/ml. During the process of arousal, there i s a r i s e of i n s u l i n , which i s c o r r e l a t e d to r e c t a l t e m p e r a t u r e . In t h e ground s q u i r r e l plasma I . R . I . l e v e l I s at 28 ~U/ml i n autumn, I t reaches 12 ~U/ml s t th e o n s e t o f h i b e r n a t i o n and i n c r e a s e s s i g n l f i c a n t l y towards t h e end o f w i n t e r . During s p r i n g th e I . R . I . l e v e l i s h i g h e r than i n w i n t e r , then In J u l y s second hypoi n s u l i n a e m i c phase can be o b s e r v e d . At t h e time of p e r i o d i c a r o u s a l th e plasma I n s u l l n i n t h e ground a q u l r r e l i s not d i f f e r e n t when toe animal arouses and when i t IS awake. A l l along h i b e r n a t i o n i n t h i s species the glucose l e v e l remains high (140 to 210 mg%) while the FFA l e v e l decreases from 27 mE% i n winter to i0 mB% during a c t i v e life. All these r e s u l t s show t h a t l e v e l s of glucose, FFA and i n s u l i n , are d i f f e r e n t in t h e two s p e c i e s and s u g g e s t t h a t i n s u l i n is not t h e cause o f hypoglycemia i n th e hypothermic garden dormouse. The g r a d u a l drop of g l y c e m i a d u r i n g t o r p o r i n th e dormouse seems t o be l i n k e d w i t h th e m a i n t e n a n c e o f l i v e r g l y c o g e n and t h e c o n t r o l l e d u t i l i z a t i o n of g l u c o s e , which i s i t s e l f r e l a t e d to th e a n l m a l ' s c o r e t e m p e r a t u r e . Moreover t h i s i n v e s t i g a t i o n i n d i c a t e s an I n t e r r e l a t l o n s h l p between plasma I n s u l l n sod FFA l e v e l s i n h i b e r n a t i n g ground squirrels.

THYROID HORMONE METABOLISM OVER THE ANNUAL CYCLE OF B.A. Demenelx and N.E. Henderson, Department o f Biology, U n i v e r s i t y o f Calgary, Calgary, Canada T2N iN4. Several aspects of t h y r o i d f u n c t i o n were examined in normothermic and t o r p i d ground s q u i r r e l s , Spe~,w?~{Zua EFFECT OF THEOPHYLLINE ~ IMIDAZOLE ON HYPOTHE~MIC ISOLATED r~ehaPd~oni. Serum t i t r e s o f TSH, T; and T 3 were measured hEARTS FROM A hIBE~NATOP ~ D A ~ONHIBERNATOR. R.F. Burlington by r a d l o l m u n o a s s a y a t monthly i n t e r v a l s o v e r th e annual and G A. Melninger. Biology Department, Central Hicbigan cycle. Blood s a mp le s were t a k e n i n t h e f i e l d between March University, Mr. Pleasant, MI 48859, USA and O c to b e r and from l a b o r a t o r y c o l o n i e s o f h l b e r n a t i n ~ and Hearts from C~teL~8 t r ~ d e e e g ~ n e a t u s and Sprague-Dawley normotbermlc s q u i r r e l s from O c to b e r to F e b r u a r y . In normoa l b l n o r a t s were p e r f u s e d w i t h a m o d i f i e d Langendorf t e c h t h e r m l c a n i m a l s , T~ c o n c e n t r a t i o n s ranged from 10 to J0 ng/

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