Regulation of hormone activityRegulation of hormone activityRegulation of hormone synthesis & releaseLevels of all hormones are regulated by gene expressionRegulatory points unique to steroid hormone synthesisRegulatory points unique to protein hormone synthesis:Slide 7Regulation of exocytosis results in pulsatile releaseRegulation by specific bloodstream proteasesRegulation by persistenceMeasuring persistenceProtein hormone half-lifeSteroid hormone inactivation by metabolismSteroid metabolism allows clearanceHormone concentration rangesConcentration is localGland size important predictor of hormone concentrationHormone amount per unit volumeTarget level regulationReceptor diversity dictates target responseMultiple hormones at the targetFeedback regulationMost hormones are regulated by negative feedbackPositive feedback is non homeostaticFeedback required for tissue homeostasisReview questionsReview questionsNotesPGY452/552: Endocrine physiologyA. Hormone synthesis & releaseB. Persistence of hormone actionC. Target level regulationD. Feedback regulation3. Regulation of hormone activityRegulation of hormone activityCoveredHormonesSignalsRegulation key to homeostasisMechanisms1. Hormone synthesis & release2. Persistence3. Target4. Feedback5. Input2HHHHHHHHHHHInputInputResponseHormoneA. Regulation of hormone synthesis & releaseSynthesis: All hormonesRelease: Only proteins3Levels of all hormones are regulated by gene expression4AAAAAAAAAAAmRNAAAAAAAAAAAA± ± GeneAAAAAAAAAAASteroidogenic cytochromes P450preprohormoneHProtein hormonesProtein hormonesDirectDirectIndirectIndirectSteroid hormonesSteroid hormonesTranscriptional regulationTranscriptional regulationPol IIRegulatory points unique to steroid hormone synthesis5P450SCCP450SCCStARStARPKAPKA PKCUnique enzymeUnique enzymePol IIP450SCCP450SCCStARStARUnique enzymeUnique enzymeFast – kinaseSlow -- transcriptionPKAPKAPKCSteroid acute regulatory proteinCytochrome P450 side chain cleavageUnique biosynthetic enzymesLDL receptorsPPLDL-RECFbloodAAAAAARegulatory points unique to protein hormone synthesis:1. Transcription of the hormone gene*2. Exocytosis of stored vesicles* 3. Proteases in the blood stream (rare)6#2 Fast#2 Fast"± ± #3 Fast#3 Fast#1Slow#1Slow± ± ± ± *UniversalPol IIVesicle release is THE critical step in protein hormone regulation7H± ± HFast: secondsMain stimuli: Ca2+Gαq → IP3Other stimuli: Ca2+ channelsMechanismsDirect activation of releaseCa2+ activated Ca2+ releaseDistinction not importantGαs → PKAAmount of hormone available for release → regulated by transcriptionRegulation of exocytosis results in pulsatile release0 120 240 360 48005101520253035Time (min.)GnRH (pg/mL)HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHInputInputHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH8Simultaneous vesicle releaseMany vesicles in each cellNot all released at onceInput strength determines amplitude releaseNew vesicles require transcriptionSLOWRegulation by specific bloodstream proteases9Active hormonesActive hormonesInactive peptide fragmentsInactive prohormonePeptides onlyOnly a couple examples – not commonPeptides onlyOnly a couple examples – not commonProteaseProteaseActivateActivateInactivateInactivateB. Regulation by persistenceThe length of time a hormone lasts in the blood stream before disposal10Measuring persistenceHalf-life: The time it takes for the concentration of a hormone to decrease by half (t½)Steroids > ProteinsConsiderable overlapSmall proteins < Large < Glycoproteins Protein hormone binding proteins  t½ 110 50 100 150 200 250 3000%10%20%30%40%50%60%70%80%90%100%5 min60 min500 minTime (min)1 10 100 10000.353.5353503500Log time (min)Log amino acid numberSteroidsPeptidesGlycoproteinsAmides+BPvenousamino acidslumen(apical)Protein hormone half-lifeSmall amount taken up by target tissuesMostly renal filtrationSmall proteins >> Large proteinsEndocytosis at luminal membrane Metabolized to amino acidsSome have specific uptake receptors: t½12HHHHHHbasolateralSteroid hormone inactivation by metabolism13cortisol allotetrahydrocortisone pregnanediol-3-glucuronideprogesteroneEtiocholanolone-3-sufateTestosteroneEnzymatic modificationPhase 1 - modificationHydroxylationOxidationReductionPhase 2 - conjugationGlucuranationSulfationOften >1 pathwayMake solubleCytochromes P450Steroid metabolism allows clearance14Other tissuesMetabolized in the liverMetabolized in the liverEliminated with bileEliminated with bileMetabolized elsewhereMetabolized elsewhereExcretedExcretedCirculating steroid hormoneHormone concentration rangesResponse strength determined by Hormone concentrationHormone efficacy (EC50)Hormones are never zero: NO ON/OFF switchesNarrow rangeConcentrations: Steroids > glycoproteins ≈ peptides150 1 10 100 1,000 10,000 100,000 1,000,000Estradiol♂Estradiol♀Testosterone ♂FSHinhibinTSHCalcitoninGlucagonInsulinSteroidsPeptidesGlycoproteinsACTHCortisollog concentration (pM)Large gland → high concentration → broad responseLarge gland → high concentration → broad responseSmall gland → low concentration → limited responseSmall gland → low concentration → limited responseResponse reflects [Hormone] Response reflects [Hormone] Concentration is local16GlandGlandTarget1Target3Target2LARGELARGETarget1Target3Target2SmallSmallTarget1Target3Target2Gland size important predictor of hormone concentration17Pineal glandHypothalamusPosterior pituitaryAnterior pituitaryHeartLiverStomach & small intestinePancreasAdrenal cortexKidneysSkinTestesAdipose tissueOvariesBlastocystPlacentaParathyroid glandsSteroids always come from big glandsProteins often from small glands or few cells in secondary endocrine tissueProteins often from small glands or few cells in secondary endocrine tissueBig glands = lots of hormoneBig glands = lots of hormoneHormone amount per unit volume[hormone]=mole/literLots of trivial unitsLiter of:Extracellular fluidBlood plasma +Interstitial fluidPlasma, blood stream, ECF