Epidermal growth factor (EGF) inhibits stimulated thyroid hormone secretion in the mouse

Pepttde~, Vol 8, pp 743-745 ~ Pergamon Journals L t d , 1987 Pnnted m the U S A

01%-9781/87 $3 00 + 00

BRIEF C O M M U N I C A T I O N

Epidermal Growth Factor (EGF) Inhibits Stimulated Thyroid Hormone Secretion in the Mouse B. A H R I ~ N 1

D e p a r t m e n t s o f S u r g e r y a n d Pharma~ ology, L u n d U n i v e r s i t y , L u n d , S w e d e n R e c e i v e d 20 J a n u a r y 1987 AHREN, B. Aptdermal growth [at tor (EGF) inhibits ~ttmulated thyrmd hormone ~e~retton m the mouse PEPTIDES 8(4) 743-745, 1987 - - I t is known that epidermal growth factor (EGF) inhibits iodide uptake m the thyroid folhcular cells and lowers plasma levels of thyroid hormones upon infusion into sheep and ewes. In this study, the effects of EGF on basal and stimulated thyroid hormone secretion were investigated in the mouse Mice were pretreated w~th ~2~Iand thyroxine, the subsequent release of '2~I is an estimation of thyroid hormone secretion It was found that basal radlolodme secretion was not altered by intravenous rejection of EGF (5/xg/ammal). However, the radlolodine secretion stimulated by both TSH (120 /zU/ammal) and vasoactwe mtestmal peotlde (VIP, 5/zg/ammal) were inhibited by EGF (5 txg/anlmal). At a lower dose level (0 5 p~g/ammal), EGF had no influence on stimulated radlolodme secretion In conclusion, EGF inhibits stamulated thyroid hormone secretion m the mouse. EGF

Thyroid hormone secretion

VIP

TSH

In vlvo

IT is known that high affinity receptors for epidermal growth factor (EGF) exist in thyroid follicular cells [11] and that E G F is a mitogemc substance in the thyroid [8-10]. E G F has also been demonstrated to impair follicular cell iodide uptake [ 10] and upon infusion of E G F into sheep and ewes, lowered plasma levels of thyroid hormones have been observed [5,7]. This latter effect has been interpreted as being a consequence of both inhibited thyroid hormone secretion and exaggerated peripheral deiodmation of the hormones [5]. In order to study the direct effects of E G F on stimulated thyroid hormone secretion, we undertook the present investigation on the influence of E G F on radioiodine release from radJoiodme-labelled thyroids stimulated by either TSH or vasoactlve intestinal peptide (VIP).

Mouse

16/xCl Na1251 (RadIochemical Centre, Amersham, England) m 0. ! ml saline 2 days prior to the experiments and SC with 20 /xg L-thyroxine (British Drug Houses Ltd, Poole, England) in 0.1 ml saline 48 and 2 hr before the experiments. Blood (100/zl) was sampled by orbital puncture before and 2 hr after an IV injection and the radioactivity was measured in an autogamma spectrometer. The following substances were injected IV' natural ovine TSH (thyroid stimulating hormone; Ferrmg, Malmo, Sweden; 120/zU/animal), synthesized porcine VIP (vasoactlve intestinal peptide, Bacchem Inc., Torrance, CA; 5 /xg/ammal), synthesized E G F (epidermal growth factor; Chemlcon AB, Malmo, Sweden, 5 or 0.5 /zg/animal) or a combination of the substances. Controls were injected with saline with the addition of 1 g/1 gelatine, TSH, VIP, and E G F were all diluted in saline-gelatine.

METHOD

AntmalLs

St¢lllstlcs

Female mice of the NMRI strain (AnUcimex, Stockholm, Sweden) weighing 20-25 g were used. They were given an iodine-poor diet (Astra-Ewos, Sodertalje, Sweden) for 10 days prior to the injection of Na125I in order to enhance the thyroidal uptake of radioiodlne

The difference between the blood radioiodine determinations m the samples taken 2 hr after and before the IV rejection is a reflection of stimulation of thyroid hormone secretion [6] since a large fraction (24%) of the liberated radiolodine is in the form of thyroid hormones and this fraction increases upon stimulation [2]. The degree of the stimulation Is expressed as the quotient between the radioactivity in the 2 hr sample divided by the radioactivity m the initial sample × 100 (= % CPM ratio). Thus, 100% means no stlmu-

Expertments The secretion of thyroid hormones was investigated according to McKenzle [6]. Each ammal was injected IP with

~Requests for reprints should be addressed to Dr Bo Ahr6n, Department of Pharmacology, Solvegatan 10, S-223 62 Lund, Sweden

743

744

AHRISN

I

TSH

TABLE 1 CHANGES IN BLOOD RADIOACTIVITY IN MICE PRETREATED WITH Nal2-'l AND THYROXINE AFTER IV INJECTION OF SALINEGELATINE, TSH (120 p.U/ANIMAL) OR VIP (5 tzg/ANIMAL) WITHOUT OR WITH ADDITION OF EGF (5/xg/ANIMAL)

I

350" _T_

~3000

Group

% CMP Ratio

E 250-

Sahne Sahne + EGF TSH TSH + EGF VIP V1P + EGF

t.)

~200-

I

VIP

I

t£1

~ 150c~ 10050

NI ns

<0001

I----] Controt

II

101 99 286 275 139 136

_+ 3 _+ 2 +_ 18 _+ 20 _+ 4 _+ 5

Values are mean + SE of% CMP ratio in samples taken 2 hr after and immedmtely before the IV injection There were 18-20 ammals m each group

<002 EGF

FIG 1 Changes m blood radioactivity m mice pretreated with Na ~2~1 and thyroxine after IV lnjectton of sahne-gelatlne, TSH (120 /zU/anlmal) or VIP (5 /xg/ammal) without or with the addmon of EGF (5/xg/ammal) Values are mean-+SE of% CPM ratio m samples taken 2 hr after and immediately before the IV mjectmn There were 26-30 ammals m each group P indicates the probabdlty level of random d~fference between the appropriate groups n s. =not significant

lation a n d v a l u e s a b o v e 100%, v a r i o u s d e g r e e s o f s t l m u l a h o n o f t h y r o i d h o r m o n e s e c r e t m n . M e a n s - + S E are g w e n Stud e n t ' s t-test w a s u s e d for t e s t s of significance b e t w e e n groups. RESULTS

Effe~ ts o f E G F on Basehne Radiomdme Levels N e i t h e r at 5 p~g/ammal (Fig. 1), n o r at 0.5 p~g/antmal (Table 1), did E G F affect b a s e l i n e r a d m l o d m e levels d u r i n g the 2 h r period studied.

Effects o# E G F on TSH-Stlmulated Radtotodme Levels T S H e n h a n c e d r a d l o i o d i n e levels by 324+ 1 I% ( p < 0 . 0 0 1 ) . E G F (5 p~g/anlmal) r e d u c e d this s t i m u l a t i o n to 260-+15%. T h u s , E G F i n h i b i t e d T S H - i n d u c e d t h y r o i d h o r m o n e secret m n ( p < 0 . 0 0 1 ) (Fig. 1). A t the low d o s e o f 0 5 /xg/animal, E G F did n o t affect T S H - i n d u c e d t h y r o i d h o r m o n e s e c r e t i o n (Table 1).

( p < 0 . 0 2 ) (Fig. 1) In c o n t r a s t , at 5 /zg/ammal, E G F did not influence V I P - m d u c e d t h y r o i d h o r m o n e s e c r e t i o n (Table 1). DISCUSSION E G F Is k n o w n to inhibit f o l h c u l a r cell iodide u p t a k e a n d t h y m i d i n e i n c o r p o r a t i o n [10,11] E G F h a s also b e e n s h o w n to inhibit the effects o f T S H o n f o l h c u l a r cell m e m b r a n e p o t e n t i a l [4]. In vlvo, E G F h a s b e e n d e m o n s t r a t e d to l o w e r p l a s m a levels of t h y r o i d h o r m o n e s u p o n infusion m s h e e p a n d e w e s [5,7], effects i n t e r p r e t e d as b e i n g c a u s e d by inhibited t h y r o i d h o r m o n e s e c r e h o n a n d e x a g g e r a t e d h o r m o n e d e i o d i n a t l o n [5] W e s h o w h e r e t h a t E G F inhibits T S H - l n d u c e d t h y r o i d h o r m o n e s e c r e t i o n m the m o u s e . W e also d e m o n s t r a t e that t h y r o i d h o r m o n e s e c r e t i o n i n d u c e d by V I P is also i n h i b i t e d b y E G F . V I P is a n l n t r a t h y r o i d a l n e u r o p e p t i d e t h a t p o t e n t l y s t i m u l a t e s t h y r o i d activity [1] a n d e v i d e n c e exists t h a t V I P a n d T S H s t i m u l a t e t h y r o i d h o r m o n e s e c r e t i o n b y at least partially d i f f e r e n t m e c h a n i s m s [1]. W e i n t e r p r e t the inhibition as b e i n g c a u s e d specifically b y E G F a n d not b y an unspecific p e p t i d e effect since earlier o t h e r p e p t l d e s h a v e b e e n s h o w n n o t to affect t h y r o i d h o r m o n e s e c r e t i o n u n d e r t h e s e c o n d i t i o n s [3] W e c o n c l u d e t h a t E G F inhibits t h y r o i d h o r m o n e secretion u n d e r m vivo c o n d m o n s W h e t h e r this i n h i b i t o r y effect o f E G F is e x e r t e d b y a d i r e c t effect o n the follicle cell or w h e t h e r the effect is m e d i a t e d b y o t h e r i n h i b i t o r y subs t a n c e ( s ) r e m a m s to b e studied.

ACKNOWLEDGEMENTS

EfJects oJ E G F on V1P-Sttmulated Radtotodlne Level~ V I P e n h a n c e d radlolodIne levels b y 120-+4%` ( p < 0 . 0 1 ) . E G F ( 5 / ~ g / a m m a l ) r e d u c e d this i n c r e a s e to 104-+5%. T h u s , EGF abolished the VIP-mduced thyroid hormone secretion

The technical assistance of Lena Kvlst is gratefully acknowledged The work was supported by the Swedish Medical Research Council, Stockholm, Sweden (Project 14X-6834) and by the Medical Faculty, Lund Umversity, Lund, Sweden.

REFERENCES

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EGF AND THYROID HORMONE SECRETION

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