- Email: [email protected]
Are arachidonic acid metabolites involved in VIP stimulated prolactin release from rat lactotrophs (GH4C1 cells)?
142 ARE ARACHIDONIC ACID METABOLITES INVOLVED IN VIP STIMULATED PROLACTIN RELEASE FROM RAT LACTOTROPHS (GH4C, CELLS)? T. BJ~RO 1&2, V. LARSEN 1, P. TORJESEN 1, O. SAND 3 a n d E. HAUG 1 , Hormone L a b o r a t o r y , A k e r Hospital, 2 D e p a r t m e n t of Clinical C h e m i s t r y , The National Hospital a n d ~ I n s t i t u t e of P h y s i o l o g y , U n i v e r s i t y of Oslo, Oslo, Norway VIP stimulates p r o l a c t i n (PRL) r e l e a s e from c u l t u r e d r a t p i t u i t a r y tumour cells (GH4C1 cells) in a dose d e p e n d e n t way. The e f f e c t s a r e mediated via cAMP a n d also b y an i n c r e a s e in i n t r a c e l l u l a r Ca 2÷ c o n c e n t r a t i o n (Bjcro et a l . , 1987). Activation of e n d o c r i n e cells i n c r e a s e t h e metabolism of a r a c h i d o n i c acid which can be metabolized to biological active s u b s t a n c e s b y t h e c y c l o o x y g e n a s e , t h e l i p o x y g e n a s e a n d t h e e p o x i g e n a s e p a t h w a y s . P h o s p h o l i p a s e A2 (PLA~) stimulated PRL r e l e a s e from GH4C1 cells dose d e p e n d e n t . The e f f e c t s of d i f f e r e n t i n h i b i t o r s of PLA2 ( q u i n a c r i n e ) , c y c l o o x y g e n a s e (indometacin, ETYEA) a n d l i p o x y g e n a s e ( n a f a z a t r o m , ETYEA) on basal a n d VIP stimulated PRL r e l e a s e w e r e s t u d i e d . T h e s e i n h i b i t o r s had little o r no e f f e c t s on basal PRL r e l e a s e b u t q u i n a c r i n e , ETYEA a n d nafazatrom all i n h i b i t e d VIP stimulated PRL r e l e a s e . T h e y also i n h i b i t e d t h e e f f e c t s of o t h e r s t i m u l a t o r y s e c r e t a g o g u e s ( t h y r o l i b e r i n , KC1, f o r s k o l i n a n d 8-Br-cAMP) on PRL r e l e a s e . Indometacin p o t e n s i a t e d VIP stimulated PRL r e l e a s e . T h e s e r e s u l t s indicate t h a t l i p o x y g e n a s e p r o d u c t s might be i n v o l v e d in the r e g u l a t i o n of PRL r e l e a s e . Bjoro et a l . , Mol. Cell. Endocrinol. 49 (1987) 119-128.
SECOND MESSENGERS IN VIP-MEDIATED SPHINCTER (LES) AND PYLORUS.
RELAXATION OF THE CAT LOWER ESOPHAGEAL
P. BIANCANI, C. HILLEMEIER, B.Y. RHIM, S. SZEWCZAK, and J. BEHAR. Rhode Island Hospital and Brown University, Providence, RI and University of Michigan, Ann Arbor, MI, USA. VIP may be a neurotransmitter responsible for relaxation of some gastrointestinal sphincters. It is known to activate adenylate cyclase causing formation of cAMP. We now show that it also reduces inositol triphosphate (IP3) levels in the LES and pylorus. Contraction of LES and pylorus depends on intracellular calcium release through an IP3 mediated pathway since: i) In muscle cells isolated by enzymatic digestion from LES and pylorus, incubation in Ca++ free physiologic solution (PS) abolished contraction of esophagus and duodenum but not of LES or pylorus. 2) Incubation in Sr++, which inhibits release of intracellular calcium, abolished contraction in LES and pylorus, but not in esophagus and duodenum. 3) After permeabilization with saponin and incubation in Ca++ free PS, LES but not esophageal cells contracted in response to IP3. The contraction was antagonized by the naphthalanesulphonamide W7, which in normal Ca++ PS blocked LES, but not esophageal contraction in response to Ach. Thus, LES contraction in response to Ach depends on IP3 mediated release of intracellular Ca++. IP3 resting levels, measured by ion exchange chromatography, were at least 3 times greater in LES and pylorus than in all other tissues. Upon stimulation with VIP, inositol phosphates decreased in LES and pylorus, while tissue levels of cAMP increased, preceding the onset of LES and pyloric relaxation. These data suggest that tone and response to Ach in the LES and pylorus depend on release of intracellular calcium through an IP3 dependent pathway, and that VIP induced relaxation may be associated both with an increase in cAMP and a concomitant decrease in IP3.
SECOND MESSENGERS IN VIP-MEDIATED SPHINCTER (LES) AND PYLORUS.
RELAXATION OF THE CAT LOWER ESOPHAGEAL
P. BIANCANI, C. HILLEMEIER, B.Y. RHIM, S. SZEWCZAK, and J. BEHAR. Rhode Island Hospital and Brown University, Providence, RI and University of Michigan, Ann Arbor, MI, USA. VIP may be a neurotransmitter responsible for relaxation of some gastrointestinal sphincters. It is known to activate adenylate cyclase causing formation of cAMP. We now show that it also reduces inositol triphosphate (IP3) levels in the LES and pylorus. Contraction of LES and pylorus depends on intracellular calcium release through an IP3 mediated pathway since: i) In muscle cells isolated by enzymatic digestion from LES and pylorus, incubation in Ca++ free physiologic solution (PS) abolished contraction of esophagus and duodenum but not of LES or pylorus. 2) Incubation in Sr++, which inhibits release of intracellular calcium, abolished contraction in LES and pylorus, but not in esophagus and duodenum. 3) After permeabilization with saponin and incubation in Ca++ free PS, LES but not esophageal cells contracted in response to IP3. The contraction was antagonized by the naphthalanesulphonamide W7, which in normal Ca++ PS blocked LES, but not esophageal contraction in response to Ach. Thus, LES contraction in response to Ach depends on IP3 mediated release of intracellular Ca++. IP3 resting levels, measured by ion exchange chromatography, were at least 3 times greater in LES and pylorus than in all other tissues. Upon stimulation with VIP, inositol phosphates decreased in LES and pylorus, while tissue levels of cAMP increased, preceding the onset of LES and pyloric relaxation. These data suggest that tone and response to Ach in the LES and pylorus depend on release of intracellular calcium through an IP3 dependent pathway, and that VIP induced relaxation may be associated both with an increase in cAMP and a concomitant decrease in IP3.