Brain Neuropeptides in Regulation of Growth and Reproduction in Pigs

Br ain h orm on es exq uisitely r egu late the secr etion of ho rm ones s ecreted by th e p ituitary g lan d that affect gr owth, metabolism , and repr odu ction . Ox ytocin w as on e o f the firs t neur oen docrine hor mo nes is olated and ch aracterized in 1 955 . Cu rr ently, 5 0 neur opeptide ho rmo nes r ang in g f rom mo no amines to p oly peptides w ith > 5,000 mo lecular weigh t have been is olated and characterized . We fo cus on o ur recen t stud ies co ncern ing h orm ones aff ectin g g row th in yo un g p igs an d tho se th at reg ulate repr odu ction . Som atic gro wth in vertebr ates is tho ug ht to be depen dent on pituitar y gro wth ho rm one (G H) ; w ith ou t p itu itary GH p rod uctio n o r p er iph eral action, po stnatal gr owth is sev erely stunted . For exam ple, a deficiency in G H p ro ductio n or GH recep tor ( GHR) g en e h as been demon strated to stunt g row th. You ng pigs req uire GH pr od uction and secretio n f ro m the pituitar y gland fo r co ntinu ed gr owth ( nitro gen r etention ); hy po phy secto my ar rests gr ow th. G H rep lacem ent th er apy in hy po phy secto mized pigs cau ses s ign if icant gr owth b ut at less er rate than in sham o perated co ntr ols . GH is s ecr eted into th e per iph er al blo od in an pu ls atile pattern in yo ung p igs an d th is ep iso dic G H s ecretion w anes w ith m atu rity. Hy po phy seal stalk tr an sectio n elimin ates pu ls atile GH secretion but b asal GH s ecr etion in th es e anim als allo ws co ntinu ed gro wth at a less er rate than s een in con tro ls. Episod ic GH secr etion was ob liter ated by hyp othalamic deaf fer entation in y oun g p ig s. In tr avenou s injectio n o f the br ain p eptide, GHreleasin g ho rm one (G HRH), stim ulates p eak release of G H s ecr etion in hy po phy seal stalktr ans ected pigs similar to th at in sh amop er ated con tro ls. Our recent exp er iments indicate that in tr avenou s injectio n o f a G H-s ecr etago gue caus es im med iate peak GH release, and co ad min istratio n o f GHRH and th e G Hsecr etagog ue au gments G H r eleas e. I ntr acerebro ven tr icu lar in jection of th e G Hsecretag ogu e cau ses a do sedep en den t in cr eas e in GH release, wh er eas central ad minis tration of so matos tatin (S RIH ) sup press es peak GH release ind uced by th e GHsecretag ogu e. Neur opeptide Y and galanin caus e mo dest GH release co mpared w ith th e GHsecretag ogu e. Lu teinizin g hor mon e releas in g h orm on e ( LHRH) is a hy po thalam ic decapep tid e pro duced by a placode of LHRH neur ons th at is cr ucial fo r go nadotrop in (LH and fo llicle stim ulatin g hor mon e, FS H) release by th e p ituitary g lan d in th e pig . Neur osu rgical interv ention s as des cr ibed abo ve ob liter ate LHRH release th us in ter ferin g w ith epis od ic LH an d FS H secretio n r equ ir ed for continu ed repro du ctive fu nction in male an d f em ale pigs .